FR3036401A1 - INK BASED ON SILVER NANOPARTICLES - Google Patents

Abstract

The present invention relates to ink formulations based on dispersions of silver nanoparticles. In particular, the present invention relates to stable inks and high concentration of silver nanoparticles.

Description

The present invention relates to ink formulations based on silver nanoparticles and more particularly to ink formulations based on dispersions of silver nanoparticles. BACKGROUND OF THE INVENTION In particular, the present invention relates to stable inks and high concentration of silver nanoparticles. Similar inks have already been described by the Applicant in his patent application PCT / EP2014 / 075416 filed on November 24, 2014. More particularly, the present invention relates to ink formulations based on silver nanoparticles, the said inks being characterized by a set of improved properties among which we will quote for illustrative purposes: - An improved disposability (as demonstrated for example by means of photos of the "drop watcher" type for the shape of the drops and / or printing tests to compare the obtained resolution), and / or improved homogeneity (as demonstrated for example by means of profilometer-type measurements), and / or - increased conductivity (as demonstrated for example by means of the "Spin Coater" and by comparison of the resistance values) -carred), and / or - Decreased volatility and / or better disposability (as demonstrated for example by means of print tests).

More particularly, the present invention relates to the field of conductive nanoparticle-based inks suitable for many printing methods. By way of nonlimiting examples, mention may be made of the following printing methods: inkjet, spray, screen printing, gravure printing, flexography, doctor blade, spin coating, and slot die coating; the inkjet application being particularly suitable for the type of ink claimed. The inks based on conductive nanoparticles according to the present invention can be printed on all types of supports. Examples include the following: polymers and polymer derivatives, composite materials, organic materials, inorganic materials.

Inks based on conductive nanoparticles according to the present invention have many advantages among which we will cite by way of non-limiting examples: a longer time stability than current inks; - versatility in their field of application; a non-toxicity of solvents and nanoparticles; a conservation of the intrinsic properties of the nanoparticles; and, in particular, - preservation of electronic properties, and - improved conductivity for annealing temperatures below 200 ° C and more particularly for annealing temperatures of less than or equal to 150 ° C. This improved conductivity is generally demonstrated by measuring the square strength of the material. The present invention also relates to an improved method of preparing said inks; Finally, the present invention also relates to the use of said inks in the fields of printed electronics (for example RF1D (Radio Frequency Identification) supports), photovoltaics, OLEDs (organic light-emitting diode), sensors (eg gas sensors), touchscreens, biosensors, and contactless technologies. At the sight of the literature of recent years, conductive colloidal nanocrystals have received a lot of attention thanks to their new optoelectronic, photovoltaic and catalytic properties. This makes them particularly attractive for future applications in the field of nanoelectronics, solar cells, sensors and biomedical. The development of conductive nanoparticles makes it possible to resort to new implementations and to foresee a multitude of new applications. The nanoparticles have a very important surface / volume ratio and the substitution of their surface by surfactants leads to the change of certain properties, especially optical properties, and the possibility of dispersing them. Their small dimensions can lead in some cases to quantum confinement effects. Nanoparticles are compounds of which at least one of their dimension is less than 100 nm. They can have different shapes: beads (from 1 to 100 nm), rods (L <200 to 300 nm), wires (a few hundred nanometers or even a few microns), discs, stars, pyramids, Tetrapods, cubes or crystals when they do not have a predefined shape.

Several methods have been developed for synthesizing conductive nanoparticles. These include, but are not limited to: - physical processes: chemical vapor deposition (also known as "Chemical Vapor Deposition - CVD") when a substrate is exposed to volatilized chemical precursors that react or decompose on its surface. This process generally leads to the formation of nanoparticles whose morphology depends on the conditions used; thermal evaporation; Molecular beam epitaxy (also known as "Molecular Beam Epitaxy") when atoms which will constitute the nanoparticles are bombarded at high speed on the substrate (where they will be fixed), in the form of a gaseous flow; - chemical or physicochemical processes: microemulsion; The laser pulse in solution, when a solution containing a precursor is irradiated with a laser beam. The nanoparticles form in the solution along the light beam; Microwave irradiation synthesis; ^ Oriented synthesis assisted by surfactants; Ultrasound synthesis; Electrochemical synthesis; Organometallic synthesis; Synthesis in an alcoholic medium; ^ Sol-gel chemistry; Oxidation-reduction synthesis. Physical syntheses consume more raw materials with significant losses. They generally require time and high temperatures which make them unattractive for the transition to production on an industrial scale. This makes them unsuitable for certain substrates, for example flexible substrates. In addition, the syntheses are carried out directly on the substrates in frames with reduced dimensions. These production methods are relatively rigid and do not produce on large substrates.

3036401 4 5 Chemical syntheses have many advantages. The first is to work in solution, the conductive nanoparticles thus obtained are already dispersed in a solvent which facilitates storage and use. In most cases, the nanoparticles are not attached to a substrate which gives more latitude in their use. These methods also allow better control of the raw materials used and limit losses. A good adjustment of the synthesis parameters leads to a good control of the synthesis and kinetics of growth of the conductive nanoparticles. This makes it possible to guarantee good batch reproducibility as well as good control of the final morphology of the nanoparticles. The delicate part is to obtain stable colloidal solutions over time without aggregation of the nanoparticles or precipitation. The customization of the surface of the nanoparticles makes it possible to fight this phenomenon effectively by choosing for this stabilizing entities such as ligands. These ligands prevent risks of aggregation and sedimentation. They offer a second advantage by also impacting the properties of the ink formulated based on these conductive nanoparticles. It is thus possible to adjust the nature of the ligands according to the intended application. In the context of biomedical application, it is thus preferred ligands such as peptides that increase the biocompatibility of nanoparticles in the biological medium. In the case of the printed electronics industry, this paves the way for the use of substrates of different sizes and types. Finally, these synthetic methods make it possible to produce stable solutions of nanoparticles in a relatively short time. All these points emphasize the strengths and flexibility of chemical synthesis routes to consider nanoparticle production on an industrial scale. It is an object of the present invention to overcome one or more disadvantages of the prior art by providing a high concentration, stable silver nanoparticle dispersion-based ink, said inks having significant improvements in the field of their application. disposability and / or their homogeneity and / or conductivity as well as decreased volatility. According to an embodiment of the present invention, this objective is achieved by means of an ink based on silver nanoparticles whose composition comprises A. a dispersion of silver nanoparticles in a content of between 5 and 60% by weight. weight, said dispersion comprising a. a compound "a" consisting of silver nanoparticles, 3036401 5 5 b. a compound "b" consisting of a cyclooctane solvent, c. a compound "c" consisting of a dispersing agent, and d. a compound "d" consisting of a dispersing agent different from the compound "c"; B. a compound "e" consisting of a solvent different from the compound "b" in a content greater than 10% by weight and less than 80% by weight; C. an optional "f" compound consisting of a rheology modifier in a content of less than 20% by weight, D. an optional "g" compound consisting of an antioxidant in a content of less than 10% by weight, and E. an "X" compound consisting of a solvent in a content of between 0.5 and 60% by weight, said ink composition being characterized in that - the compound "X" is a cyclooctane solvent, and compound "e" is a terpene alcohol, or a mixture of terpene alcohol and aliphatic monohydric alcohol, or a mixture of terpene alcohol and glycol and / or glycol ether, or a mixture of terpene alcohol and aliphatic monohydric alcohol and glycol and / or glycol ether.

The Applicant has unexpectedly discovered that the specific combination of the ink components according to the present invention made it possible to obtain inks based on dispersions of silver nanoparticles in high concentrations and with improved stability. The viscosity of the ink according to the present invention is preferably between 1 and 10 000 mPa.s, more preferably between 1 and 1000 mPa.s, for example between 2 and 20 mPa.s. This makes this ink particularly attractive for use in the fields of printed electronics (eg RFID (Radio Frequency Identification)), photovoltaics, OLEDs (organic light emitting diodes), sensors (eg sensors gas), touch screens, biosensors, and contactless technologies; the inkjet application being particularly suitable for the type of ink claimed.

The compound "a" according to the present invention therefore consists of silver nanoparticles. According to an alternative embodiment of the present invention, the objectives of the present invention are particularly well achieved when the compound "a" consists of silver nanoparticles whose dimensions are between 1 and 50 nm, preferably between 2 and 20 nm. The size of the nanoparticles is defined as the average diameter of the silver-containing particles, excluding stabilizers, as determined for example by transmission electron microscopy. According to an alternative embodiment of the present invention, the silver nanoparticles are of spheroidal and / or spherical shape. For the present invention and the claims which follow, the term "spheroidal" means that the shape resembles that of a sphere but is not perfectly round ("quasi-spherical"), for example an ellipsoidal shape . The shape of the nanoparticles is usually identified by means of microscopic photographs. Thus, according to this embodiment of the present invention, the nanoparticles have diameters of between 1 and 50 nm, preferably between 2 and 20 nm. According to a particular embodiment of the present invention, the silver nanoparticles were previously synthesized by chemical synthesis. Any chemical synthesis may be preferentially used in the context of the present invention. In a preferred embodiment according to the present invention the silver nanoparticles are obtained by a chemical synthesis which uses as silver precursor an organic or inorganic silver salt. By way of non-limiting example, mention may be made of silver acetate, silver nitrate, silver carbonate, silver phosphate, silver trifluorate, silver chloride, sodium perchlorate and the like. money, alone or in combination. According to a preferred variant of the present invention, the precursor is silver acetate.

According to a preferred embodiment of the present invention, the silver nanoparticles are thus synthesized by chemical synthesis, by reducing the silver precursor by means of a reducing agent in the presence of the dispersing agent referred to as the " c "of the present invention; this reduction can be carried out in the absence or in the presence of a solvent (hereinafter also referred to as the "synthesis solvent"). When the synthesis is carried out in the absence of solvent, the dispersing agent generally acts both as a dispersing agent and as a solvent for the silver precursor; a particular example of synthesis of nanoparticles in a solvent-free medium and preparation of the dispersion according to the present invention is described by way of illustration below. Preparation of the dispersion of the nanoparticles in the solvent "b": in a reactor containing silver acetate, the synthetic dispersing agent (compound "c", for example dodecylamine) is added in excess and the mixture is stirred. The reducing agent hydrazine is then rapidly added to the mixture and the mixture is stirred for about 60 minutes. The mixture is treated by the addition of methanol (or any other suitable solvent, for example another monohydric alcohol having 2 to 3 carbon atoms, for example ethanol) and the supernatant is removed during several washes successive (silver nanoparticles thus formed remain in the state of dispersion and in contact with liquid). The cyclooctane solvent (compound "b") is added and the residual methanol is evaporated. The compound "d" (a dispersing agent different from the compound "b" used, for example an octylamine) is then added and the mixture is stirred for 15 minutes at room temperature. The silver nanoparticle dispersions thus obtained are used directly for the formulation of conductive inks.

In general, when the synthesis is carried out in the presence of solvent, the silver precursor is dissolved in said synthetic solvent; preferably, this synthetic solvent is different from the compound "b" (hereinafter also referred to as the "dispersion solvent"). The synthesis solvent is preferably an organic solvent selected from the following list of hydrocarbons: alkanes having from 5 to 20 carbon atoms, which are exemplified by Pentane (C5H12), Hexane (C6H14), Heptane ( C7H16), Octane (C8H18), Nonane (C9H20), Decane (C10H22), Undecane (C11H24), Dodecane (C12H26), Tridecane (C13H28), Tetradecane (C14H30), Pentadecane (C15H32), Cetane (C16H34), Heptadecane (C17H36), Octadecane (C18H38), Nonadecane (C19H40), Eicosane (C20H42), Cyclopentane (C5H10), Cyclohexane (C6H12), Methylcyclohexane (C7H14); cycloheptane (C7H14), cyclononane (C9H18), cyclodecane (C10H20); aromatic hydrocarbons having 7 to 18 carbon atoms, for example toluene, xylene, ethylbenzene or ethyltoluene; and - their mixtures.

According to an essential embodiment of the present invention, at least one dispersing agent (the compound "c") is also present in addition to the silver precursor (and the synthesis solvent when the latter is used).

This dispersing agent, which we will call a synthetic dispersing agent corresponding to the above-mentioned compound "c", is preferably chosen from the list of dispersing agents described hereinafter in the present description. According to a preferred embodiment of the present invention, the silver nanoparticles are thus synthesized by chemical synthesis, by reducing the silver precursor by means of a reducing agent in the presence of the synthetic dispersing agent (the compound "c"), all of which is preferably carried out in the synthesis solvent. This synthesis is preferably carried out under non-binding pressure and temperature conditions as defined hereinafter in the present description. The reducing agent may be selected from a wide range of compounds for reducing the silver precursor. By way of illustration, mention may be made of the following compounds: hydrogen; hydrides, among which we will mention by way of example NaBH4, LiBH4, KBH4, and tetrabutylammonium borohydride; the hydrazines, among which we will mention by way of example hydrazine (H2N-NH2), substituted hydrazine (methylhydrazine, phenylhydrazine, para-methoxyphenylhydrazine, dimethylhydrazine, diphenylhydrazine, etc.), hydrazine salt (substituted), etc ... amines, among which we will mention by way of example trimethylamine, triethylamine, etc ...; and their mixtures. In general, after the reduction step, the nanoparticles are then subjected to a washing / purification step that removes anything that is not chemically or physically related to the nanoparticles. According to a particular embodiment of the present invention, a liquid phase is always present, both during the reduction step of the silver precursor and during all the steps (for example the washing and purification steps). above) that precede the addition of compound "b" (cyclooctane). In other words, a preferred feature of the present invention is that the silver nanoparticles are never isolated and dried; they therefore preferably remain in contact with a liquid phase (for example a solvent) in which they are dispersed. As demonstrated further in the description, this characteristic makes it possible to considerably improve certain properties (monodispersion, homogeneity, stability and lower temperature annealing) of the silver nanoparticles. This approach eliminates the isolation step of the nanoparticles which has a positive impact in terms of production costs and health and safety of people. The compound "b" according to the present invention therefore consists of a cyclooctane solvent. The compounds "c" (synthetic dispersing agent) and "d" (dispersing agent) according to the present invention therefore consist of dispersing agents characterized in that the dispersing agent "d" is different from the agent "c" used. This difference is displayed by a different chemistry; for example, a different carbon chain length (for example a difference of at least two carbon atoms in the chain), and / or a linear carbon chain compound and the other not, and / or a Cyclic carbon chain and the other not and / or an aromatic carbon chain compound and the other not. According to a preferred embodiment of the present invention, the compound "c" has a molecular weight and / or a length of carbon chain at least 20% greater than that of the compound "d", for example at least 40% higher. These dispersing agents may advantageously be selected from the families of organic dispersing agents which comprise at least one carbon atom. These organic dispersing agents may also comprise one or more nonmetallic heteroatoms such as a halogenated compound, nitrogen, oxygen, sulfur, silicon. As examples, thiols and their derivatives, amines and their derivatives (for example amino alcohols and ethers of amino alcohols), carboxylic acids and their carboxylate derivatives, polyethylene glycols and / or mixtures thereof are exemplary. In a preferred embodiment of the present invention, the organic dispersing agents "c" and "d" will be selected from the group consisting of amines such as for example propylamine, butylamine, pentylamine, hexylamine, hexamethylamine and the like. heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, hexadecylamine, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminononane, diaminodecane, dipropylamine dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, methylpropylamine, ethylpropylamine, propylbutylamine, ethylbutylamine, ethylpentylamine, propylpentylamine, butylpentylamine, tributylamine, trihexylamine, or mixtures thereof.

According to a preferred embodiment of the present invention, the compounds "b" (cyclooctane) and "d" are added to the silver nanoparticles already synthesized in the presence of the compound "c". This addition usually takes place after the washing / purification steps of the nanoparticles as described in the present description.

A particular example of synthesis of nanoparticles and preparation of the dispersion according to the present invention is described by way of illustration below: Preparation of the dispersion of the nanoparticles in the solvent "b" (cyclooctane). In a reactor containing silver acetate in toluene, the synthetic dispersing agent (compound "c", for example dodec) is added and the mixture is stirred.

The hydrazine reducing agent is then rapidly added to the mixture and the mixture is allowed to stir for about 60 minutes. The mixture is treated by the addition of methanol (or any other suitable solvent, for example another monohydric alcohol having 2 to 3 carbon atoms, for example ethanol) and the supernatant is removed during three washes successive (silver nanoparticles thus formed remain in the state of dispersion and in contact with liquid, in this case in contact with methanol). The cyclooctane solvent (compound "b") is added and the residual methanol is evaporated. The compound "d" (a dispersing agent different from the compound "b" used, for example an octylamine) is then added and the mixture is stirred for 15 minutes at room temperature. The silver nanoparticle dispersions thus obtained are used directly for the formulation of the conductive inks. According to a preferred embodiment of the present invention the nanoparticles which are used are characterized by D50 values (which can be measured for example by means of the method described below) which are preferably between 2 and 12 nm; they are also preferably characterized by a monodisperse (homogeneous) distribution without aggregate. For the nanoparticles synthesized in the presence of solvent, the preferred range of D50 will be between 2 and 8 nm; for the nanoparticles synthesized in the absence of a solvent, the preferred range of D50 will be between 5 and 12 nm. The dispersion thus obtained may be used directly or diluted to obtain the desired properties before being incorporated, for example, into an ink. However, and this represents a considerable advantage of the dispersions according to the present invention, said dispersions are characterized by superior stability (before dilution) as demonstrated in the examples. According to one embodiment of the present invention, the dispersion of silver nanoparticles comprises a compound "a" (silver nanoparticles) in a content of greater than 30% by weight, preferably greater than 35% by weight. , for example greater than 40% by weight, - a compound "b" (cyclooctane) in a content of between 20 and 65% by weight, preferably between 40 and 60% by weight, - a compound "c" (dispersing agent ) in a content between 3 and 15% by weight, preferably between 3 and 10% by weight, and - a compound "d" (dispersing agent different from the compound "c") in a content of between 0.1 and 15% by weight, preferably between 0.4 and 5% by weight. According to one embodiment of the present invention, the dispersion of silver nanoparticles may also include in its composition additional compounds among which we will mention by way of example solvents (for example ethers, alcohols, esters, and / or additives (for example polymers) whose objective may be for example the improvement of the dispersion of the nanoparticles. However, the compounds "a", "b", "c", and "d" (within the ranges of proportions indicated above) will preferably comprise at least 55% by weight of the final dispersion, preferably at least 75% by weight, for example at least 90% by weight, at least 95% by weight, at least 99% by weight, or even 100% by weight of the final dispersion. According to one embodiment of the present invention, the dispersion of silver nanoparticles does not include water in its composition. However, since the components of the dispersion can tolerate traces of water depending on their degree of purity, it goes without saying that the sum of these corresponding traces of water will be acceptable in the dispersions of silver nanoparticles according to the present invention. Thus, the water content in the final dispersion generally depends essentially on the water content of the solvents used for its preparation; the monohydric alcohol (the dispersion washing methanol in our example embodiment above) will have this citrate the most important impact - compared with the other solvents used in the preparation of the dispersion - on the final water content of the dispersion. According to a particular embodiment of the present invention, the dispersions of silver nanoparticles 3036401 comprise water concentrations of less than 2% by weight, preferably less than 1% by weight, for example less than 0.5. % by weight, or even less than 0.2% by weight. According to a preferred embodiment of the present invention, with the exception of traces of water possibly present in the formulation / dispersion preparation compounds, water is not added during the formulation of dispersions. of silver nanoparticles. The compound "e" present in the ink according to the present invention therefore consists of a solvent different from the compound "b" (cyclooctane) used and its content in the ink is greater than 10% by weight and less than 80% by weight. ; said compound "e" is a terpene alcohol, or a mixture of terpene alcohol and aliphatic monohydric alcohol, or a mixture of terpene alcohol and glycol and / or glycol ether, or a mixture of terpene alcohol and aliphatic monohydric alcohol and glycol and / or glycol ether.

According to one embodiment of the present invention, this solvent compound "e" is a terpene alcohol selected from the family of menthol, nerol, cineol, lavandulol, myrcenol, terpineol (alpha-, beta-, gamma-terpineol, and and / or terpinen-4-ol, preferably alpha-terpineol), isoborneol, citronellol, linalool, borneol, geraniol, and / or a mixture of two or more of said alcohols.

According to one embodiment of the present invention, this solvent compound "e" is a mixture of terpene alcohol as defined above and aliphatic monohydric alcohol which is divided among the group consisting of ethanol, propanol, butanol. , pentanol and hexanol and their isomers (eg isopropanol, tert-butanol), and / or a mixture of two or more of said aliphatic monohydric alcohols.

According to one embodiment of the present invention, this solvent compound "e" is a mixture of terpene alcohol as defined above and glycol and / or glycol ether which will preferably be selected - for the glycols among which we will mention by way of example ethylene glycol, propylene glycol, diethylene glycol, hexylene glycol, trimethylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, pentamethylene glycol for the glycol ethers among the mono- or di-ethers of glycols, among which mention may be made by way of example of ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, and the like; ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol propyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol propyl ether ethylene glycol di-methyl ether, ethylene glycol di-ethyl ether, ethylene glycol di-butyl ether, glymes, diethylene glycol diethyl ether, di-butylene glycol diethyl ether, diglymes, ethyl diglyme, butyl diglyme), and / or a mixture of two or more of said glycol and / or glycol ethers. According to one embodiment of the present invention, this solvent compound "e" is a mixture of terpene alcohol as defined above and aliphatic monohydric alcohol as defined above and glycol and / or glycol ether as defined above.

According to one embodiment of the present invention, the ink is characterized in that the compound "e" is a mixture of terpene alcohol and aliphatic monohydric alcohol whose weight ratio [terpene alcohol] / [monohydric alcohol] aliphatic] is between 1/6 and 11/1, for example between 1/1 and 11/1. According to one embodiment of the present invention, the ink is characterized in that the compound "e" is a mixture of terpene alcohol and glycol and / or glycol ether whose weight ratio [terpene alcohol ] / [glycol and / or glycol ether] is between 1/6 and 11/1, for example between 1/1 and 11/1. According to one embodiment of the present invention, the ink is characterized in that the content of terpene alcohol (compound "e") is greater than or equal to 30% by weight.

The optional compound "f" according to the present invention therefore consists of a rheology modifier. By way of example, mention may be made of cellulose-type agents, for example alkyl cellulose, preferably ethylcellulose, nitro-celluloses, and / or mixtures thereof. The optional compound "g" according to the present invention therefore consists of an antioxidant. Examples are: ascorbic acid or vitamin C (E300), sodium ascorbates (E301), calcium (E302), diacetyl 5-6-1-ascorbic acid (E303), palmityl acid 6-1- ascorbic acid (E304); citric acid (E330), sodium citrate (E331), potassium (E332) and calcium (E333); Tartaric acid (E334), sodium tartrates (E335), potassium (E336) and sodium and potassium tartrates (E337); butylhydroxyanisole (E320) and butylhydroxytoluol (E321); 30 - octyl (E311) or dodecyl (E312) gallates; - sodium lactate (E325), potassium (E326) or calcium (E327); Lecithins (E322); natural tocopherols (E306), synthetic α-tocopherol (E307), synthetic γ-tocopherol (E308) and synthetic 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. According to a particular embodiment of the present invention, the ink compositions also comprise an additional solvent, which we will call "X" solvent which is cyclooctane. Three particular examples of preparation of the ink according to the present invention are described by way of illustration hereinafter 1) in a reactor containing the solution of silver nanoparticles in dispersion (mixture of the compounds "a", "b", "c "And" d ") is added a mixture of solvent" e 20 "and" X "and the whole is stirred for 15 min at room temperature. 2) in a reactor containing a mixture of solvent "e" is added with stirring and at room temperature a cellulosic rheology-modifying agent (compound "f"). To this solution is added the compound "X" and the whole is stirred for 15 min at room temperature. This mixture is then added to the dispersed silver nanoparticle solution (mixture of compounds "a", "b", "c", and "d") and the whole is stirred for 15 min at room temperature. 3) in a reactor containing a mixture of solvent "e" and "X" is added with stirring and at room temperature an antioxidant (compound "g"). This mixture is then added to the dispersed silver nanoparticle solution (mixture of compounds "a", "b", "c", and "d") and the whole is stirred for 15 min at room temperature. According to a particular embodiment of the present invention, the inks formulated according to the present invention contain a content of less than 60% by weight of nanoparticles (compound "a"), preferably between 5 and 45%, and more particularly between 10 and 40% by weight. According to one embodiment of the present invention, the silver ink comprises a dispersion according to the present invention (with the compounds "a", "b", "c" and "d"), in a content of less than or equal to 60% by weight, and preferably greater than 5% by weight, preferably greater than 10% by weight, for example greater than 20% by weight and even greater than 40% by weight, compound "e" in a content of greater than 10% by weight and less than 80% by weight, preferably less than 70% by weight, preferably between 15 and 65% by weight, - a compound "f" (modifying agent rheology) in an amount of less than 20% by weight, preferably between 0.1 and 2% by weight, an optional "g" compound consisting of an antioxidant in a content of less than 10% by weight, preferably less than 3% by weight, and - an "X" compound (cyclooctane) in an inferior content. 60% by weight, preferably less than 41% by weight, and preferably greater than 0.5% by weight. According to one embodiment of the present invention, the ink may also include in its composition other compounds among which we will mention by way of example additives (for example, an additive of the family of silanes) whose The objective may for example be to improve the resistance to different types of mechanical stress, for example adhesion to many substrates; the following substrates may be mentioned as examples: polyimide, polycarbonate, PET polyether tetraphthalate), polyethylene naphthalate (PEN), polyaryletherketone, polyester, thermostabilized polyester, glass, ITO glass, AZO glass, SiN glass. However, the compounds "a", "b", "c", "d", "e", "f", "g" and "X" (in the ranges of proportions indicated above) will preferably be less than 50% by weight of the final ink, preferably at least 75% by weight, for example at least 90% by weight, at least 95% by weight, at least 99% by weight, or even 100% by weight of the final ink. According to one embodiment of the present invention, the ink does not include water in its composition. However, since the ink components can tolerate water traces depending on their degree of purity, it is understood that the sum of these corresponding water traces will be acceptable in the inks according to the present invention. Thus, the water content in the final ink generally depends essentially on the water content of the solvents used for its preparation; the monohydric alcohol (the dispersion washing methanol in our example embodiment above) will have the highest impact on this citrate - compared to the other solvents used in the preparation of the ink - the final water content of the ink. According to a particular embodiment of the present invention, the inks comprise water concentrations of less than 2% by weight, preferably less than 1% by weight, for example less than 0.5% by weight, or even lower. at 0.2% by weight. According to a preferred embodiment of the present invention, with the exception of traces of water possibly present in the compounds of formulation / preparation of the ink, water is not added during the formulation of the inks . According to an alternative embodiment of the present invention, the preparation of the nanoparticle dispersion according to the present invention is characterized by the following steps: a. synthesizing the silver nanoparticles in the presence of the dispersing agent (compound "c") by reduction using a reducing agent of a silver precursor; b. washing / purification of the nanoparticles obtained in step "a", c. additions of compound "b" and compound "d". According to a preferred embodiment of the present invention, a liquid phase is always present during all these preparation steps. In other words, a preferred characteristic according to the present invention is that the silver nanoparticles are never isolated and dried; they therefore preferably remain in contact with a liquid phase (for example a solvent) in which they are dispersed. According to a preferred embodiment of the present invention, during step "a", the addition of the reducing agent is carried out in any suitable container (for example a reactor) with the characteristic that it is carried out sub-level, for example using a plunger directly introduced into the reaction medium. An additional advantage of the dispersion according to the present invention lies in the fact that its preparation can be carried out under non-binding pressure and / or temperature conditions, for example at pressure and / or temperature conditions close to normal conditions or ambient. It is preferable to remain within 40% of normal or ambient pressure conditions and, with respect to temperature, the latter is generally below 80 ° C, preferably below 70 ° C. For example, we have found that it is preferable to maintain the pressure conditions during the preparation of the dispersion at values at most 30%, preferably 15%, around normal pressure conditions. or ambient, preferably near atmospheric pressure. A control of these pressure and / or temperature conditions can therefore advantageously be included in the device for preparing the dispersion so as to fulfill these conditions.

This advantage related to a preparation of the dispersion under non-binding conditions obviously also results in a facilitated use of said dispersions. According to an alternative embodiment of the present invention, the preparation of the nanoparticle-based ink according to the present invention is characterized by the following consecutive steps: a. introduction of the compound "e" into a container, and b. addition of the dispersion according to the present invention in said container. The ink thus obtained can be used directly or diluted to obtain the desired properties.

According to a particular embodiment of the present invention, when a rheology modifying agent (compound "f") is used in the composition of the ink, the preparation of the nanoparticle ink according to the present invention is characterized by the following consecutive steps: a. use of the compound "f" in a mixture of compounds "e" and "X", and b. addition of the dispersion according to the present invention. An additional advantage of the ink according to the present invention lies in the fact that its preparation can be carried out under non-constraining pressure and / or temperature conditions, for example at pressure and / or temperature conditions close to or identical to the normal or ambient conditions. It is preferable to remain within 40% of normal or ambient pressure and / or temperature conditions. For example, the Applicant has found that it is preferable to maintain the pressure and / or temperature conditions during the preparation of the ink at values oscillating at most 30%, preferably 15% around the values of the conditions. normal or ambient. A control of these pressure and / or temperature conditions can therefore be advantageously included in the ink preparation device so as to fulfill these conditions. This advantage related to a preparation of the ink under non-binding conditions obviously also results in a facilitated use of said inks. According to an embodiment of the present invention, the ink may advantageously be used in any printing method, in particular inkjet, spray, screen printing, gravure printing, flexography, doctor blade, spin coating, and slot die coating. ; The inkjet application being particularly suitable for the type of ink claimed. It is therefore obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the scope of the invention as claimed. Therefore, the present embodiments should be considered by way of illustration but may be modified in the field defined by the scope of the appended claims. The present invention and its advantages will now be illustrated by means of the formulations listed in the table below. The dispersion synthesis and the ink formulations were prepared in accordance with the embodiments described above in the description. The chemical compounds used are indicated in the first row of the table. The square resistance of the ink as mentioned in the present invention may be measured by any suitable method. By way of example corresponding to the measurements given in the table, it can be advantageously measured according to the following method: An ink deposited by spincoating on a substrate (600 rpm / 3 min - for example glass), is subjected to a annealed with a hot plate or oven. An analysis of the square resistance is carried out under the following conditions: Device reference: S302 Resistivity Stand 4-tip head reference: SP4-40045TFY 30 Current source reference: Agilent U8001A Meter reference: Agilent U3400 Measurement temperature: Room temperature Coefficient According to an alternative embodiment of the present invention, the Applicant has found that the square resistance values (measured as described above) of the inks obtained in accordance with the present invention were preferably less than 50%. 100 mohms / sq for thicknesses greater than or equal to 1 μm (annealing temperature 3036401 at 150 ° C). This particular square strength property gives the inks of the present invention improved conductivity for annealing temperatures of less than 200 ° C and more particularly for annealing temperatures of 150 ° C or lower (as demonstrated in the Example and measured). The silver nanoparticle content as mentioned in the present invention may be measured to any appropriate extent. By way of example corresponding to the measurements given in the table, it can advantageously be measured according to the following method: Thermogravimetric analysis Apparatus: TGA Q50 of TA Instrument 15 Crucible: Alumina Method: ramp Measuring range: from room temperature to 600 ° C. Temperature rise: 10 ° C / min The size distribution of the silver nanoparticles (in the D50 dispersion) as mentioned in the present invention can be measured by any suitable method. By way of example, it can be advantageously measured according to the following method: use of a device of the Nanosizer S type of Malvem with the following characteristics: DLS (Dynamic light scattering) measurement method: - Type of vessel: optical glass - Material: Ag - Refractive index of nanoparticles: 0.54 - Absorption: 0.001 30 - Dispersant: Cyclooctane - Temperature: 20 ° C - Viscosity: 2.133 - Dispersant refractive index: 1.458 - General Options: Mark-Houwink parameters 35 - Analysis Model: General Purpose - Equilibration: 120 s - Number of measurements: 4 3036401 20 Figures 1 and 2 are representative of a general example of DLS spectrum (Dynamic light scattering) obtained during the synthesis of the nanoparticles according to the present invention respectively with synthetic solvent (Figure 1) and when the dispersing agent is used as the synthesis solvent (Figure 2). We can see the particle size spectra in the size (in nm) of the silver nanoparticles.

Figure 1 - D50: 5.6 nm Figure 2 - D50: 8.0 nm Dso is the diameter for which 50% of the silver nanoparticles in number are smaller. This value is considered representative of the average grain size.

The viscosity of the ink as mentioned in the present invention may be measured by any suitable method. By way of example, it can advantageously be measured according to the following method: Apparatus: AR-G2 Rheometer from TA Instrument Conditioning time: Pre-shear at 40 s-1 for 10 seconds / equilibration for 1 minute Type of test: Shear bearings Bearings: 40 s-1, 100 s-1 and 1000 s-1 Duration of a step: 5 minutes Mode: linear 25 Measurement: every 10 seconds Temperature: 20 ° C Curve reprocessing method: Newtonian Retarded Area: The Entire Curve The surface tension of the ink as mentioned in the present invention may be measured by any suitable method. By way of example, it can be advantageously measured according to the following method: Apparatus: OCA 15 of Appolo Instrument Method: Drop pending 35 Reprocessing: Laplace-Young Volume: 0.2 'IL 3036401 21 5 Flow rate: 1 .tL / s Diameter needle: 1.65 mm Temperature: 20 ° C Formulations - Table Ex Ag CO Dodecylamine Octylamine CO Butanol "e" DEGDBE alpha-hexylene "b" "c" "d" "X" "e" terpineol glycol "e" "e" Comp. 22.1 2 0.3 30.6 20 5 0 0 F1 20 22.1 2 0.3 0.6 0 0 50 5 F2 20 22.1 2 0.3 0.6 5 0 50 0 10 Ag = Silver nanoparticles (D50: 8.0 nm) CO = Cyclooctane DEGDBE = Diethylene Dibutyl ether glycol The viscosity and surface tension values of the inks are shown in the table below. Name Viscosity Surface tension Comp. 2.5 cP 26 mN / m F1 15.4 cP 26 mN / m F2 13.1 cP Not yet measured It can be seen that the viscosity is higher for Fl and F2 which improves the flowability (see also Figure 3 ). Jet and splat diameter tests were also performed for these three inks. A visual representation is given in Figure 3. It can be seen that the disposability is improved between the comparative formulation and the ink formulation F 1 according to the present invention because the drops are better aligned (visual inspection). Similarly, the disposability is even better for the ink formulation F2car the drops are even better aligned. The square resistance was measured according to the protocol described above (600 rpm 3 min, annealing 150 ° C 30 min). The values are shown in the table below.

3036401 22 5 Ex. Thickness Square resistance (mOhm / square) Comp. 0.28 μm 200 F1 0.4 1.1.m 260 F2 0.35 μm 181 Spin-coating Deposition tests were also performed for these three inks. A visual representation is given in FIG. 4. The spin-coating deposits are of better quality for examples F1 and F2 (more homogeneous deposit, brighter, mirror effect) than for the comparative example. 15

Claims (15)

REVENDICATIONS1. An ink based on silver nanoparticles whose composition comprises A. a dispersion of silver nanoparticles in a content of between 5 and 60% by weight, said dispersion comprising 10 a. a compound "a" consisting of silver nanoparticles, b. a compound "b" consisting of a cyclooctane solvent, c. a compound "c" consisting of a dispersing agent, and d. a compound "d" consisting of a dispersing agent different from the compound "c", B. a compound "e" consisting of a solvent different from the compound "b" in a content of greater than 10% by weight and less than 80% by weight C. an optional compound "f" consisting of a rheology modifier in a content of less than 20% by weight, D. an optional "g" compound consisting of an antioxidant in a content of less than 10% by weight and E. an "X" compound consisting of a solvent in a content of between 0.5 and 60% by weight, said ink composition being characterized in that the compound "X" is a cyclooctane solvent, and the compound "e" is a terpene alcohol, or a mixture of terpene alcohol and aliphatic monohydric alcohol, or a mixture of terpene alcohol and glycol and / or glycol ether, or a mixture of of terpene alcohol and aliphatic monohydric alcohol and glycol t / or glycol ether. 2. Ink according to the preceding claim characterized in that the organic dispersing agents "c" and "d" are amines, preferably amines selected from the group consisting of propylamine, butylamine, pentylamine, hexylamine, amine heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, hexadecylamine, diaminopentane, diaminohexane, diaminoheptane, diaminooctane, diaminononane, diaminodecane, dipropylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, methylpropylamine, ethylpropylamine, propylbutylamine, ethylbutylamine, ethylpentylamine, propylpentylamine, butylpentylamine, tributylamine, trihexylamine, or a mixture of two or more of these compounds. 3. Ink according to any one of the preceding claims, characterized in that the dispersion of silver nanoparticles comprises the compound "a" (silver nanoparticles) in a content of greater than 30% by weight, preferably greater than 35%. % by weight, for example greater than 40% by weight, the compound "b" (cyclooctane) in a content of between 20 and 65% by weight, preferably between 40 and 60% by weight, the compound "c" (dispersing agent) in a content of between 3 and 15% by weight, preferably between 3 and 10% by weight, and the compound "d" (dispersing agent different from the compound "c") in a content of between 0, 1 and 15% by weight, preferably between 0.4 and 5% by weight. 4. Ink according to any one of the preceding claims characterized in that the compounds "a", "b", "c", and "d" constitute at least 55% by weight of the dispersion, preferably at least 75% by weight, for example at least 90% by weight, at least 95% by weight, at least 99% by weight, or even 100% by weight of the dispersion. 5. Ink according to any one of the preceding claims characterized by a viscosity of between 2 and 20 mPa.s. 6. Ink according to any one of the preceding claims characterized in that the terpene alcohol (compound "e") is selected from the family of menthol, nerol, cineol, lavandulol, myrcenol, terpineol (alpha-, beta-, gamma-terpineol, and / or terpinen-4-ol, preferably alpha-terpineol), isoborneol, citronellol, linalool, terminalol, geraniol, and / or a mixture of two or more of said alcohols, - alcohol aliphatic monohydrogen (compound "e") is selected from the group consisting of ethanol, propanol, butanol, pentanol and hexanol and their isomers and / or a mixture of two or more of said alcohols, 3036401 25 - the glycol is selected among ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, 1,3-butylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, pentamethylene glycol, hexylene glycol and / or a mixture of two or more of glycols, and the glycol ether ( e "e") is selected from mono- or di-ethers of glycols, for example 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, propylene glycol methyl ether, propylene glycol butyl ether, propylene glycol propyl ether, ethylene glycol di-methyl ether, ethylene glycol di-ethyl ether, ethylene glycol di-butyl ether, glymes, diethylene glycol diethyl ether, di-butylene glycol diethyl ether, diglymes, ethyl diglyme, butyl diglyme), and / or a mixture of two or more of said glycol ethers. Ink according to any one of the preceding claims, characterized in that the compound "f" (rheology modifying agent) is present and is selected from cellulose-type agents, for example alkyl-cellulose, preferably ethylcellulose, nitro-celluloses, and / or mixtures thereof. 8. Ink according to any one of the preceding claims, characterized in that it comprises - the dispersion in a content greater than 10% by weight, for example greater than 20% by weight, - the compound "e" in a content between 15 and 65% by weight, - the compound "f" optional in a content of less than 2% by weight, - the compound "g" optional in a content of less than 3% by weight, and - the compound "X" in a content of less than 60% by weight, preferably less than 41% by weight, and in a content of greater than 0.5% by weight. 9. Ink according to any one of the preceding claims, characterized in that the weight ratio [terpene alcohol] aliphatic monohydric alcohol] is between 1/6 and 11/1. 3036401 26 5 Ink according to any one of the preceding claims, characterized in that the weight ratio [terpene alcohol] / [glycol ether] is between 1/6 and 11/1. 11. Ink according to any one of the preceding claims, characterized in that the content of terpene alcohol (compound "e") is greater than or equal to 30% by weight. 10 12. Ink according to any one of the preceding claims, characterized in that the compounds "a", "b", "c", "d", "e", "f", "g" and "X" constitute less than 50% by weight of the final ink, preferably at least 75% by weight, for example at least 90% by weight, at least 95% by weight, at least 99% by weight, or even 100% by weight of the final ink. 15 Ink according to any one of the preceding claims, characterized in that it comprises a water content of less than 2% by weight, preferably less than 1% by weight, for example less than 0.5% by weight, or even less than 0.2% by weight. 14. A process for preparing the ink according to any one of the preceding claims, characterized in that the dispersion of nanoparticles is prepared according to the following steps: a. synthesizing the silver nanoparticles in the presence of the dispersing agent (compound "c") by reduction using a reducing agent of a silver precursor; B. washing / purification of the nanoparticles obtained in step "a", c. additions of the compound "b" and the compound "d", and characterized in that a liquid phase is always present during these preparation steps. 15. Use of an ink according to any one of claims 1 to 13 in an ink jet printing application.