Silver nanowire-based inks

Abstract

The present invention relates to silver nanowire-based ink formulations, in particular to silver nanowire ink formulations, which are stable, transparent and have improved electrical conductivity.

Description

[Technical field]

[0001] The present invention relates to ink formulations based on silver nanowires. In particular, the present invention relates to ink formulations based on silver nanowires, said inks being stable, transparent and having improved electrical conductivity. The present invention also relates to the use of the claimed silver nanowire-based inks for the fabrication of transparent conductive elements by additive manufacturing, in particular by screen printing, and to the fabrication of transparent conductive electrodes from the claimed silver nanowire-based inks.

[0002] Transparent conductive films (referred to as "TCFs" in the following description) are used in a wide range of products such as liquid crystal displays ("LCDs"), touch screens (phones, tablets, Global Positioning Systems (denoted by the abbreviation "GPS"), ...), organic light emitting diodes or "OLEDs" for lighting (usually referred to by the English acronym "OLED" for organic light emitting diode), solar cells (both organic and silicon) and optical devices.

[0003] These TCFs are very attractive, considering the huge market of the products in which they are incorporated. This TCF market is mainly occupied by indium-tin oxide (known by its English acronym "ITO" for "indium tin oxide"), because ITO allows to achieve a very good sheet resistance, or as it is called in French "resistance carrée" (as low as 10 Ω / □), and also allows a very high transparency, two important criteria for TCFs. However, ITO has two drawbacks: 1) ITO films are not very flexible, and the sheet resistance increases sharply with the radius of curvature, making it unsuitable for flexible applications; 2) indium, one of the three components of ITO, is a substance that does not exist in reserves by itself, but is extracted (in very small quantities) as a by-product of zinc mining. Moreover, none of the top three indium producing countries are European (China, Canada and Japan account for about 75% of the world production). It is therefore identified by the European Union as one of the 14 main raw materials.

[0004] Related to this ITO alternative, the applicant has developed conductive transparent inks that can advantageously replace existing technologies while offering other advantages enumerated herein. These inks can be advantageously used as transparent electrodes and / or heating circuits in markets such as 5G smartphones and "wearables" (an English acronym for which the Academie Française has yet to find a French synonym, which the inventors translate as "wearable connected objects"). Among the claimed inks, some (especially those containing metal oxide nanoparticles) have also been designed and developed to improve the manufacturing costs of transparent conductive layers (for charge transport, e.g. "ETL" for "electron transport layer" and / or "HTL" for "hole transport layer") for, for example, organic solar cells (usually referred to by its English acronym "OPV" for "organic photovoltaic cell"), OLED, flat panel display and optical markets. Furthermore, and this constitutes one embodiment of the present invention, the claimed inks are particularly suitable for use in the field of screen printing, allowing to directly print transparent conductive designs by additive manufacturing.

[0005] Chinese patent application CN107365529(A) claims a conductive ink useful for preparing reel-to-reel conductive films, characterized in that it comprises, in weight percentages: 5-50% nano silver wire dispersion, 0.1-5% conductive polymer, 0.01-0.5% silane coupling agent, 0.1-5% viscosity modifier, 5-40% organic solvent, 5-40% deionized water, 0.1-5% polymer resin, 0.1-5% pH adjuster, 0.1-0.5% non-ionic surfactant, 0.01-0.5% wetting and dispersing agent, 0.01-0.5% leveling agent, 0.01-0.5% defoamer, and 0.01-1% metal nanoparticles. Summary of the Invention

[0006] ink The present invention relates to a compound comprising the following as a main compound: a. at least 0.1 wt. % silver nanowires; b. at least 0.75% by weight of a monohydric alcohol having 1 to 4 carbon atoms, preferably isopropyl alcohol; c. at least 2% by weight of hydroxypropyl methylcellulose; d. at least 20% by weight water; e. at least 20% by weight ethylene glycol, and f. at least 10% by weight of propylene glycol propyl ether; The ink comprises at least 60% by weight of the ink in total.

[0007] According to one embodiment of the invention, the total of the main ink compounds comprises at least 65% by weight of the claimed ink, such as at least 75% by weight of the ink, preferably at least 90% by weight.

[0008] The development of this ink formulation faces many technical problems, among which foam formation and drying are mentioned by way of example.

[0009] In fact, it was not the choice of solvent, nor the choice of antifoam agent, but the combination of all the main compounds and their claimed contents that resulted in the optimum formulations claimed.

[0010] Thus, and this constitutes one embodiment of the present invention, the ink formulation is also characterised 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.

[0011] Thus, and this constitutes one embodiment of the present invention, the ink formulation is also characterised in that the weight ratio between ethylene glycol and propylene glycol propyl ether ((ethylene glycol) / (propylene glycol propyl ether)) is between 0.5 and 2, for example between 1.0 and 1.8.

[0012] Ink Viscosity According to one embodiment of the present invention, 40s -1The viscosity of the ink, measured at a shear rate of 100 to 50,000 mPa.s and at 20°C, is preferably 200 to 10,000 mPa.s, for example 400 to 2,000 mPa.s. The viscosity can be measured by any suitable method. By way of example, the viscosity can advantageously be measured using the following method: Machine: TA Instrument AR-G2 Rheometer Conditioning time: 100s -1 3 min preshear / 1 min equilibration Test type: Shear process Steps: 10s -1 , 40s -1 , 100s -1 and 1000s -1 Process duration: 5 minutes Mode: Linear Measurement: Every 10 seconds ·Temperature: 20℃ Curve reprocessing method: Newton method Processing area: Entire curve.

[0013] Silver Nanowires The ink according to the invention comprises at least 0.1% by weight of silver nanowires. In the context of the present invention, any type of silver nanowires can be advantageously used. The concentration of said silver nanowires in the ink is advantageously limited to 2% by weight of the ink. According to one embodiment of the present invention, the concentration of silver nanowires in the ink is between 0.15% and 1% by weight. More particularly, silver nanowires with an average nanowire length of 5-50 μm, preferably 10-30 μm and / or an average nanoparticle diameter of 15-60 nm, preferably 20-40 nm are preferred.

[0014] The characterization of the nanowire size can be carried out by any suitable method. The following method is mentioned by way of example: images are taken by microscope, in particular by field emission scanning electron microscope (FE-SEM), measurements are carried out in ultra-high resolution mode (FoV=50 μm) at electron energy of 10 keV and various magnifications ranging from 7,000x to 350,000x. An averaging is carried out on a number of nanowires, for example 30 nanowires, representative of the majority of the nanowires, making it possible to establish an average nanowire length and / or diameter.

[0015] Silver nanowires, which may be preferred for the purposes of the present invention, are generally available in the form of a dispersion in a solvent such as isopropyl alcohol (herein referred to as "IPA") and / or water, with the concentration of these silver nanowires in the solvent preferably being greater than 0.5% by weight, e.g., greater than 0.8% by weight (weight of nanowires / (weight of solvent+weight of nanowires)).

[0016] Monohydric Alcohols The ink according to the invention comprises at least 0.75% by weight of a monohydric alcohol having 1 to 4 carbon atoms. This alcohol is advantageously selected from aliphatic monohydric alcohols, for example selected from the group consisting of methanol, ethanol, propanol and butanol, and / or mixtures of two or more of said aliphatic monohydric alcohols, isopropyl alcohol being the preferred alcohol. The concentration of the monohydric alcohol in the ink is advantageously limited to 5% by weight of the ink. According to one embodiment of the invention, the concentration of the monohydric alcohol in the ink is between 1% and 2% by weight.

[0017] HPMC The ink according to the 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. According to one embodiment of the invention, the concentration of HPMC in the ink is between 2.5% and 3.5% by weight. Hydroxypropyl methylcellulose, also known as hypromellose, is an inert viscoelastic cellulose ether.

[0018] It is well known and widely used in the pharmaceutical, food (E464) and construction industries.

[0019] Hydroxypropyl methylcellulose which may be preferred in the context of the present invention has the following characteristics: an HPMC methoxy group content of 20 to 40% by weight, preferably 27 to 30% by weight, and / or - HPMC hydroxypropoxy group content between 5 and 15% by weight, preferably between 7 and 12% by weight.

[0020] Hydroxypropyl methylcellulose, which may be preferred in the context of the present invention, is generally available in the form of an aqueous solution. Preferably, a solution containing 5 to 20% by weight of hydroxypropyl methylcellulose in water, for example about 12% by weight in water, is used. 40s of an aqueous solution of hydroxypropyl methylcellulose (12% by weight) -1 The viscosity measured at the shear rate and at 20°C is preferably 20 to 50 Pa.s at 20°C, for example 25 to 35 Pa.s at 20°C.

[0021] water The ink according to the 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. According to one embodiment of the invention, the concentration of water in the ink is between 30% and 40% by weight.

[0022] Ethylene glycol The ink according to the 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. According to one embodiment of the invention, the concentration of ethylene glycol in the ink is between 30% and 40% by weight.

[0023] Ethylene glycol, also known as glycol or ethane-1,2-diol, is primarily used in (petro)chemistry as an antifreeze, coolant and reagent.

[0024] Although the ink composition according to the invention may contain other polyols as a replacement for ethylene glycol (not recommended) or as a complement to ethylene glycol (as optional compounds), the Applicant has found that ethylene glycol should be preferred in order to optimally respond to the technical challenges and the required objectives (e.g. drying, foaming, conductivity, ...).

[0025] Preferred polyols are those having a boiling point below 260° C. Examples that may be mentioned include glycols such as propylene glycol, diethylene glycol, trimethylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, pentamethylene glycol, hexylene glycol, ... and / or mixtures of two or more of the aforementioned compounds.

[0026] According to one embodiment of the invention, when the ink composition comprises, in addition to ethylene glycol, other polyols (optional compounds used), it is advantageously ensured that the ratio of the total weight of said optional polyols in the ink composition divided by the weight of ethylene glycol in the ink composition is less than 50%, for example less than 30% or even less than 10%.

[0027] Propylene glycol propyl ether The ink according to the 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. According to one embodiment of the invention, the concentration of propylene glycol propyl ether in the ink is between 20% and 35% by weight. In the examples, Dowanol PNP ("propylene glycol propyl ether") is advantageously used.

[0028] Although the ink composition according to the invention may contain other polyol ethers as an alternative to propylene glycol propyl ether (not recommended) or as a complement to propylene glycol propyl ether (as optional compounds), the Applicant has found that propylene glycol propyl ether should be preferred in order to optimally respond to the technical challenges and the required objectives (e.g. drying, foaming, conductivity, ...).

[0029] Preferred polyol ethers are those with a boiling point below 260° C. Examples which may be mentioned include glycol ethers, such as glycol mono- or diethers, among which 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, glyme, diethylene glycol diethyl ether, dibutylene glycol diethyl ether, dipropylene glycol monomethyl ether, diglyme, ethyl diglyme, butyl diglyme, and / or glycol ether acetates (for example 2-butoxyethyl acetate, diethylene glycol monoethyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate), and / or mixtures of two or more of the aforementioned compounds.

[0030] According to one embodiment of the present invention, when the ink composition comprises other polyol ethers (optional compounds used) in addition to propylene glycol propyl ether, it is advantageously ensured that the ratio of the total weight of said optional polyol ethers in the ink composition divided by the weight of propylene glycol propyl ether in the ink composition is less than 50%, for example less than 30% or even less than 10%. When dipropylene glycol monomethyl ether is present, the ratio of its weight divided by the weight of propylene glycol propyl ether in the ink composition is advantageously less than 10%, for example less than 5%, less than 1% or even less than 0.1%.

[0031] Optional Compounds According to one embodiment of the present invention, the claimed ink may contain up to 35% by weight of optional compounds as defined below. Among these optional compounds, the following may be mentioned by way of example: an alcohol selected from monohydric alcohols having 1 to 4 carbon atoms, different from those already used as the main compound in the ink; Antioxidants, Adhesion promoters, Defoamers, Leveling agents, compounds consisting of metal oxide nanoparticles, and / or Pigments and / or dyes.

[0032] According to one embodiment of the invention, the main compound and the optional compounds together comprise at least 95% by weight of the claimed ink, such as at least 99% by weight, preferably the entire ink.

[0033] Alcohol of your choice The inventors advantageously ensure that the ratio of the weight of the optional alcohol compound in the ink composition divided by the weight of the main alcohol compound in the ink composition is less than 30%, for example less than 10%, or even less than 5%. The alcohol used as the optional compound is for example chosen from aliphatic monohydric alcohols having 1 to 4 carbon atoms.

[0034] Optional Antioxidants According to one embodiment of the invention, the claimed ink may comprise one or more antioxidants, advantageously in a total concentration in the ink of 0.1-5% by weight.

[0035] Examples of antioxidants that may be used in the claimed inks include: · Ascorbic acid or vitamin C (E300), sodium ascorbate (E301), calcium ascorbate (E302), 5,6-di-acetyl L-ascorbate (E303), 6-palmityl L-ascorbate (E304); · Citric acid (E330), sodium citrate (E331), potassium citrate (E332) and calcium citrate (E333); · Tartaric acid (E334), sodium tartrate (E335), potassium tartrate (E336) and potassium tartrate (E337); ·Butyl hydroxyanisole (E320) and butyl hydroxytoluene (E321); · Octyl gallate (E311) or dodecyl gallate (E312); · Sodium lactate (E325), potassium lactate (E326) or calcium lactate (E327); ·Lecithin (E322); The tocopherols which together constitute vitamin E are natural tocopherol (E306), synthetic alpha-tocopherol (E307), gamma-tocopherol (E308) and delta-tocopherol (E309); eugenol, thymol and / or cinnamaldehyde, Also, mixtures of two or more of said antioxidants.

[0036] Optional Adhesion Promoter According to one embodiment of the invention, the claimed ink may comprise one or more adhesion promoters, advantageously in a total concentration in the ink of 0.1-5% by weight.

[0037] Examples of adhesion promoters that may be used in the claimed inks include those selected from synthetic polymers such as polyacrylics, polyvinyls, polyesters and / or polyurethanes, silanes, siloxanes, polysiloxanes, and / or mixtures of two or more of the aforementioned adhesion promoters.

[0038] Without intending to limit our description, these different adhesion promoters can selectively achieve good adhesion on different types of substrates such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyamide, polyimide, polyetherimide, polyurethane, polyetheretherketone, polyphenylsulfone, fluoropolymer, chloropolymer, glass, silicon, epoxy resin composites, cellulose derivatives, electrophotoactive and charge transport layers for electronic devices, silicone, metal and / or ITO based coatings, etc. Examples that may be mentioned include poly(vinylpyrrolidone-co-vinyl acetate), which provides good adhesion especially to polymeric substrates, cellulose derivatives, glass and metal coatings.

[0039] Optional Defoamer According to one embodiment of the present invention, the claimed ink may contain one or more defoamers (chemical additives), the total concentration of which in the ink is advantageously between 0.1 and 5% by weight. Without intending to limit this description, these various defoamers can be used to prevent foam formation or to destroy foam that has already formed. Examples of defoamers that may be used in the claimed ink include insoluble oils (ethylene bisstearamide (EBS), kerosene, waxes), polydimethylsiloxanes and other silicones (hydrophobic silica dispersed in silicone oils), fatty alcohols with long carbon chains (>C8), fatty esters (e.g. stearates), polyols (polyethylene glycol and polypropylene glycol copolymers), and / or mixtures of two or more of the aforementioned defoamers.

[0040] Optional Leveling Agent According to one embodiment of the invention, the claimed ink may comprise one or more levelling agents, which are chemical additives, the total concentration of which in the ink is advantageously between 0.1 and 5% by weight. Without intending to limit this description, these various levelling agents make it possible to prevent the formation of cracks and to obtain a smooth and flat coating. They are molecules with surface active properties, whose mode of action is to reduce the surface tension of the deposited ink. Examples of levelling agents that can be used in the claimed ink include silicone polyacrylates (silicone acrylate copolymers) and fluorosurfactants (surfactants containing perfluoroalkyl groups), and / or mixtures of said levelling agents.

[0041] Optional pigments and / or dyes According to one embodiment of the invention, the claimed ink may comprise one or more pigments and / or dyes, advantageously in a total concentration in the ink of 0.1-5% by weight.

[0042] Dyes are natural or synthetic organic compounds that are soluble in the medium they are to color. They are used in solutions, often aqueous.

[0043] Pigments are usually natural or synthetic inorganic compounds that are insoluble in the medium they are dispersed in. They provide a color that is unaffected, or only slightly affected, by the medium in which they are dispersed.

[0044] For example, pigments are mineral or organic white or colored particles designed to change the absorption wavelength, e.g., to change the coloration of the final dried ink film. Examples include: mineral pigments, such as titanium oxide, zirconium oxide or cerium oxide, as well as zinc oxide, iron oxide or chromium oxide, ferric blue, manganese violet, ultramarine blue and / or chromium hydrate, inorganic pigments such as carbon black, cochineal carmine, lacquers based on barium, strontium or calcium, Organic pigments, and / or mixtures of two or more of the above pigments.

[0045] According to a variant of one embodiment of the invention, the ink may also contain nacre (for example iridescent particles produced in the shells of certain mollusks or synthesized), which we call pearlescent pigments. Examples include white pearlescent pigments such as mica coated with titanium or bismuth oxychloride, colored pearlescent pigments such as titanic mica with iron oxide, especially titanic mica with ferric blue or chromium oxide, titanic mica with organic pigments of the aforementioned types, as well as pearlescent pigments based on bismuth oxychloride, and / or mixtures of two or more of the aforementioned compounds.

[0046] According to a variant of one embodiment of the invention, the ink may also contain colorless or white, mineral or synthetic lamellar or non-lamellar particles, among which, by way of example, talc, zinc stearate, mica, kaolin, polyamide powder, polyethylene powder, tetrafluoroethylene polymer powder, starch and boron nitride, polymer microspheres such as polyvinylidene chloride / acrylonitrile, acrylic acid copolymers and silicone resin microbeads, elastomeric organopolysiloxanes, and / or mixtures of two or more of the abovementioned compounds.

[0047] According to a variant of one embodiment of the invention, the ink may also contain water-soluble or liposoluble dyes, among which liposoluble dyes such as Sudan Red, DC Red 17, DC Green 6, β-carotene, soybean oil, Sudan Brown, DC Yellow 11, DC Violet 2, DC Orange 5, quinoline yellow, water-soluble dyes such as beet juice, methylene blue, and / or mixtures of two or more of the aforementioned compounds, may be mentioned by way of example.

[0048] Optional Metal Oxide Nanoparticles According to a variant of one embodiment of the invention, the claimed ink may comprise metal oxide nanoparticles, advantageously with a total concentration in the ink of 0.1-5% by weight. Examples of metal oxide nanoparticles include zinc oxide nanoparticles and / or tungsten oxide nanoparticles, and / or mixtures of the two. Examples include tungsten oxide (WO3) nanoparticles containing oxalate ligands (e.g., 5%-15% by weight of oxalate ligands) and / or zinc oxide (ZnO) nanoparticles containing acetate ligands (e.g., 5%-15% by weight of acetate ligands).

[0049] These nanoparticles can have a variety of shapes, among which, by way of example only, if they do not have a defined shape, are beads (e.g., 1-100 nm), rods (e.g., length L<200-300 nm), wires (e.g., hundreds of nanometers or even microns long), disks, stars, pyramids, tetrapods, or crystals.

[0050] According to a variant of one embodiment of the invention, the nanoparticles have a size between 1 and 50 nm, preferably between 2 and 20 nm.

[0051] According to a variant of one embodiment of the invention, the nanoparticles are spheroidal and / or spherical. In the present invention and in the following claims, the term "spheroidal" means that the shape resembles that of a sphere, but is not perfectly round ("quasi-spherical"), e.g. elliptical.

[0052] The size distribution of the nanoparticles can be measured by any suitable method. For example, it can be advantageously measured using the following method: using a Malvern Nanosizer S type machine with the following characteristics: Dynamic Light Scattering (DLS) Measurement: Cell type: Optical glass Material: Metal oxide, e.g. ZnO or WO3 Refractive index of nanoparticles: 2.008 Absorption: 0.001 Dispersant: Solvent, e.g. methanol (for ZnO) or ethylene glycol (for WO3) ·Temperature: 20℃ Viscosity: 0.5867 (for methanol) or 19.8316 (for ethylene glycol) Dispersant refractive index: 1.326 (for methanol) or 1.423 (for ethylene glycol) General options: Mark-Houwink parameters Analysis model: General purpose ·Equilibration: 120 seconds Number of measurements: 4

[0053] D50 is the diameter below which 50% of the nanoparticles are found by number. This value is considered to represent the average particle size.

[0054] The shape and size of the nanoparticles can also be advantageously identified by images taken with a microscope, in particular a transmission electron microscope (TEM), as described below. The measurements are carried out using a Thermofisher Scientific transmission electron microscope (TEM) with the following characteristics: Take bright-field (TEM-BF) images at 300 kV; Use a 50μm objective aperture at low magnification and no objective aperture at high resolution. · Dimensional measurements are made on TEM images using Digital Micrograph software and averaged over a number of particles representative of the majority of the particles, e.g. 20 particles, to establish the average area, average perimeter and / or average diameter of the nanoparticles.

[0055] Thus, according to a variant of one embodiment of the invention, the nanoparticles are spheroidal and preferably have a diameter of 1 to 20 nm. 2 , preferably 5 to 15 nm 2 and / or an average nanoparticle perimeter of 3-20 nm, preferably 5-15 nm, and / or an average nanoparticle diameter of 0.5-7 nm, preferably 1-5 nm.

[0056] Deposition method Although any deposition method can be used for the claimed inks, e.g. by adapting the viscosity and / or solids content of said inks, deposition by coating or screen printing, preferably screen printing deposition, is particularly suitable.

[0057] An example of screen printing deposition is the ATMA AT-45PA digital flatbed screen printer, which can be used to print patterns by screen printing. Screen printing is a printing technique that uses a stencil (mask) that is interposed between the ink and the substrate. The substrate used can vary (paper, cardboard, textile, metal, glass, wood, etc.). To define the pattern to be printed, the material that makes up the screen is blocked in certain areas so that the ink does not pass through them. To achieve this, the screen is coated with a photosensitive emulsion, and the areas where the ink should not pass are exposed to UV light, which hardens the emulsion. The emulsion in the areas not exposed to UV light is removed with water. The ink can then pass through the corresponding screen mesh. ATMA machines are designed to print on high-quality flat substrates such as flexible circuits, touch screens, rigid or flexible printed circuits, etc. In screen printing deposition, a quantity of ink is deposited on the mask, the squeegee and counter squeegee are impregnated with the ink, and then the ink is automatically transferred onto the substrate through the mask design.

[0058] In particular, the screen printing deposition realized within the framework of the present invention was carried out with the following printing parameters: Printing speed: 100m / s Pressure: Indicator 9 Squeegee hardness: 75 Shore -Squeegee angle: 22.5° Screen Mask Characteristics: Mesh count: 230 mesh / inch Mesh diameter: 48μm Mesh type: Polyester Emulsion thickness: 30μm

[0059] The deposit is then left to dry, for example in two steps, at room temperature for 90 seconds, followed by annealing at 90° C. for 5 minutes. This was the method used to prepare the samples whose transmittance and sheet resistance properties were measured.

[0060] transparent conductive electrode The present invention also relates to the fabrication of transparent conductive elements based on the claimed inks by additive manufacturing, preferably by screen printing.

[0061] The present invention therefore also relates to the use of the claimed silver nanowire-based ink for the preparation of a transparent conductive element by additive manufacturing, in particular by screen printing. The present invention also relates to said transparent conductive element, such as a transparent conductive electrode, produced according to any of the above listed uses, i.e. additive manufacturing, in particular by screen printing.

[0062] Any type of suitable substrate can be advantageously used for the deposition of the claimed inks, among which, by way of example, plastics such as polyester, PET (e.g. Folex® films, e.g. Folex X-130), PC, or cellulose-based materials such as paper or nanocellulose can be mentioned.

[0063] The ink is advantageously gently homogenized (e.g., manually) at room temperature for a period of time, e.g., 30 minutes, prior to use. Optionally, the ink is gravity filtered through a nylon filter of 60 μm porosity.

[0064] As already indicated above, the preferred deposition method is the screen printing method described above.

[0065] The deposit is then left to dry, for example in two steps, at room temperature for 90 seconds, followed by annealing at 90° C. for 5 minutes.

[0066] transparency The transparency of the ink is expressed by measuring the transmittance of the prepared samples as detailed in the above description.

[0067] According to one embodiment of the present invention, the transparency of the claimed ink is characterized by a sample transmittance value of 80-95% at a wavelength of 550 nm. The transmittance measurements are advantageously performed using a Varian Cary 300 UV-visible spectrophotometer (Agilent) that utilizes a halogen lamp and a deuterium (UV) lamp that allows measurements over a wavelength range of 200-800 nm (the visible range is 380-800 nm). The UV-visible spectrophotometer measures the absorbance (a unitless quantity) of a sample when a beam of light passes through it. When light of intensity I0 passes through a sample, some of it is absorbed by the sample itself. Thus, the intensity I of the transmitted light is less than I0. The absorbance of a solution is defined by the following equation:

number

[0068] The transmittance is defined by the following relationship:

number

[0069] Absorbance is a unitless positive value. It increases as the transmitted intensity decreases. The Cary 300 spectrophotometer is a double beam instrument, where the light is split into two beams before reaching the sample. One beam is used as a reference and passes through the "blank" (in the present case the substrate), while the other beam passes through the sample (metal coating on a PET substrate). The sample and the reference are positioned on a solid sample holder. The instrument alternates between measuring the transmitted beam of the reference sample and the transmitted beam of the sample under analysis. The analysis is performed in double beam mode, with a prior baseline measurement and automatic baseline correction during the sample measurement. The results are presented in the form of a graph showing the absorbance curve of the sample as a function of wavelength, which is converted to a transmittance curve using the formula above. The transmittance values ​​in the examples described in this invention are specifically obtained from measurements made at 550 nm.

[0070] conductivity The ink conductivity is expressed by measuring the sheet resistance of the prepared samples as detailed in the above description.

[0071] According to one embodiment of the present invention, the conductivity of the claimed ink is characterized by a sample sheet resistance value of 5-100 ohms / square.

[0072] The sheet resistance of conductive coatings can be advantageously measured using the four-point method. By way of example, the equipment and software used for this method is a Microworld S302 resistivity bench coupled to 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 DC current is applied to the outer probe of the measurement head, resulting in an increase in voltage between the other two points on the head. The sheet resistance is then calculated according to this formula:

number

[0073] where Rs is the sheet resistance (in ohms / □), ΔV is the voltage variation measured between the inner probes (in volts), and I is the current applied between the outer probes (in amperes). The coefficient 4.53236 is given in the S302 resistivity bench user manual and corresponds to π / ln(2)=4.53236. [Brief description of the drawings]

[0074] [Figure 1] FIG. 1 represents an example of how the advantages of the present invention can be visualized.

[0075] example Table 1 below shows three ink compositions representative of the present invention. [Table 1]

[0076] The percentages in the table are by weight.

[0077] "Ag NW" refers to silver nanowires having the following dimensions: diameter 25±3 nm and length 13±6 μm.

[0078] "IPA" is isopropyl alcohol with a purity level of 99.9% manufactured by VWR, CAS number 67-63-0, reference number 84881.

[0079] "EG" is 100% pure ethylene glycol from VWR, CAS number 107-21-1, reference number 24041.297.

[0080] "Dowanol™ PnP" is propylene glycol propyl ether, 99% pure, manufactured by DOW Inc, CAS number 1569-01-3.

[0081] "HPMC" is hydroxypropyl methylcellulose used from a 12% by weight solution of HPMC, reference 44779, from Alfa Aesar, in permeate water, reference 102928H AnalaR NormaPur grade 3 1 μS / cm max, from VWR.

[0082] "Edaplan® LA413" is a substituted polysiloxane additive from MUNZING, reference number M9586, with a purity level of approximately 100%.

[0083] Table 2 below shows the properties of the inks and the corresponding deposits. [Table 2]

[0084] PET is PET Folex X-130 (polyethylene terephthalate).

[0085] For comparison, an ink formulation was prepared identical to that in Example 2 above using ingredients selected from the prior art according to Chinese patent application CN107365529(A). [Table 3]

[0086] Both inks were deposited by screen printing and dried under exactly the same conditions as mentioned in Table 2 above. Observation using the images attached in Figure 1 shows that the deposit according to the comparative example has a heterogeneous appearance with dewetting and foaming, whereas the deposit of Example 2 has a homogeneous appearance in line with the technical effect mentioned in the introduction of the invention.

[0087] FIG. 1 is one example of how to visualize the benefits of the present invention, among which are the improved drying, lack of foaming, and uniformity of the deposit, which are important for the use of screen printing inks.

Claims

1. As the main compound, a. at least 0.1 wt. % silver nanowires; b. at least 0.75% by weight of a monohydric alcohol having 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; An ink wherein the weight percentage of each of said primary compounds is based on the total weight of the ink, and said primary compounds together comprise at least 60% by weight of the ink.

2. a weight ratio between water and ethylene glycol ((water) / (ethylene glycol)) of 0.5 to 2, for example 0.8 to 1.2, and / or 2. An ink according to claim 1, characterized in that the weight ratio between ethylene glycol and propylene glycol propyl ether ((ethylene glycol) / (propylene glycol propyl ether)) is between 0.5 and 2, for example between 1.0 and 1.

8.

3. The ink according to claim 1 , wherein the concentration of silver nanowires in the ink is 2% by weight or less.

4. The ink according to claim 1, wherein the concentration of silver nanowires in the ink is 0.15% by weight to 1% by weight.

5. 2. The ink according to claim 1, wherein the concentration of the monohydric alcohol in the ink is 5% by weight or less.

6. 2. The ink according to claim 1, wherein the concentration of the monohydric alcohol in the ink is 1% by weight to 2% by weight.

7. 2. An ink according to claim 1, characterized in that the monohydric alcohol having 1 to 4 carbon atoms is chosen from aliphatic monohydric alcohols.

8. 2. The ink of claim 1, wherein the monohydric alcohol having 1 to 4 carbon atoms is isopropyl alcohol.

9. 2. The ink according to claim 1, wherein the concentration of hydroxypropyl methylcellulose in the ink is 4% by weight or less.

10. 2. The ink according to claim 1, wherein the concentration of hydroxypropyl methylcellulose in the ink is 2.5% to 3.5% by weight.

11. 2. The ink according to claim 1, wherein the concentration of water in the ink is 50% by weight or less.

12. 2. The ink according to claim 1, wherein the concentration of water in the ink is 30% by weight to 40% by weight.

13. 2. The ink according to claim 1, wherein the concentration of ethylene glycol in the ink is 50% by weight or less.

14. 2. The ink according to claim 1, wherein the concentration of ethylene glycol in the ink is 30% to 40% by weight.

15. 2. The ink according to claim 1, wherein the concentration of propylene glycol propyl ether in the ink is 40% by weight or less.

16. 2. The ink according to claim 1, wherein the concentration of propylene glycol propyl ether in the ink is 20% by weight to 35% by weight.

17. Shearing rate 40s －１ 2. The ink of claim 1, wherein the viscosity of the ink measured at 20° C. is 400 to 2000 mPa.s.

18. 2. The ink of claim 1, wherein the silver nanowires have an average nanowire length of 5 to 50 μm and / or an average nanoparticle diameter of 15 to 60 nm.

19. 2. The ink according to claim 1, wherein the hydroxypropyl methylcellulose has a methoxy group content of 20 to 40% by weight and / or a hydroxypropoxy group content of 5 to 15% by weight.

20. 2. The ink of claim 1, wherein the total of said main compounds comprises at least 90% by weight of said ink.

21. Optional compounds include: a. an alcohol selected from monohydric alcohols having 1 to 4 carbon atoms, different from those already used as the main compound in the ink; b. antioxidants; c. adhesion promoters; d. antifoaming agents; e. leveling agent, f. Compounds consisting of metal oxide nanoparticles, and / or g. Pigments and / or dyes 2. The ink of claim 1, comprising:

22. Fabrication of transparent conductive elements based on the ink of claim 1 by screen printing.

23. 23. A transparent conductive element fabricated in accordance with claim 22.

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