EP3298088A1 - Ink comprising silver nanoparticles - Google Patents

Abstract

The invention relates to ink formulations comprising dispersions of silver nanoparticles. In particular, the invention relates to stable inks having a high concentration of silver nanoparticles.

Description

 INK BASED ON SILVER NANOPARTICLES

The present invention relates to ink formulations based on silver nanoparticles and more particularly to ink formulations based on dispersions of silver nanoparticles. 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 November 24, 2014.

 More particularly, the present invention relates to ink formulations based on silver nanoparticles, said inks being characterized by a set of improved properties, among which we will mention by way of illustration:

 Improved disposability (as demonstrated, for example, by means of "drop watcher" photos 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 profiometer measures), and / or

 Increased conductivity (as demonstrated for example by means of "Spin Coater" and by comparison of Resistance-square values), 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 numerous advantages, among which we will mention as non-limiting examples:

 a stability in time superior to 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 especially,

- a conservation of the electronic properties, and

 an 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 a method of improved preparation of said inks; Finally, the present invention also relates to the use of said inks in the fields of printed electronics (for example RFID (Radio Frequency Identification) supports), photovoltaics, OLEDs (organic light-emitting diode), sensors (eg gas sensors), touch panels, 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 interesting 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, in particular 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:

1 to 100 nm), rods (L <200 to 300 nm), wires (a few hundred nanometers even a few microns), discs, stars, pyramids, tetrapods, cubes or crystals when they have no predefined shape.

 Several processes have been developed to synthesize conductive nanoparticles. Among them, one can quote in a non-exhaustive way:

- the physical processes:

 ■ the 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;

^■ the molecular beam epitaxy (also known under the name "Molecular Beam Epitaxy") when the atoms which will constitute the nanoparticles are high-speed bombarded on the substrate (where they will bind) under the form of a stream gaseous;

- chemical or physicochemical processes:

^■ the microemulsion;

^■ the laser pulse in solution when a solution containing a precursor is irradiated with laser beam. The nanoparticles form in the solution along the light beam;

 ■ Microwave irradiation synthesis;

^■ Oriented synthesis assisted by surfactants;

^■ Synthesis under ultrasound;

^■ 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. Moreover, 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.

 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 involved 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 tricky part is to obtain stable solutions colloidally 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 quantities 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.

The present invention aims to overcome one or more disadvantages of the prior art by providing a dispersion-based ink of stable and high concentration of silver nanoparticles, said inks having significant improvements in the field of their disposability and / or their homogeneity and / or conductivity as well as reduced volatility. According to an embodiment of the present invention, this objective is achieved thanks to 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

 at. a compound "a" consisting of silver nanoparticles,

 b. a compound "b" consisting of a cyclooctane solvent,

 vs. 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 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. a compound "X" 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

 o 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 uses in the fields of printed electronics (for example RFID (Radio Frequency Identification) supports), photovoltaics, OLEDs (electroluminescent organic diode), sensors (for example gas), touch panels, 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 μm. 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 that 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 variant 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" compound. 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 medium without solvent 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 hydrazine reducing agent is then rapidly added to the mixture and the mixture is left stirring 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 may be 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 the 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 therefore 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 preferably taking place 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; 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), and the like. ; 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 eliminates 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 The preferred feature 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. As demonstrated further in the description, this characteristic makes it possible to considerably improve certain properties (monodispersion, homogeneity, stability and annealing at lower temperature) of the silver nanoparticles. This approach eliminates the nanoparticle isolation step, which has a positive impact in terms of production costs and personal health and safety.

 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 (e.g., 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 carbon chain length at least 20% greater than that of the compound "d", for example at least 40%> greater .

 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, mention may be made of thiols and their derivatives, amines and their derivatives (for example amino alcohols and amino alcohol ethers), carboxylic acids and their carboxylate derivatives, polyethylene glycols, and / or their mixtures.

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, 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, trihexyamine, 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 left stirring 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 conductive inks.

According to a preferred embodiment of the present invention, the nanoparticles that 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 nanoparticles synthesized in the presence of a 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 can be used directly or diluted to obtain the desired properties before being incorporated, for example, in 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 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 of 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 of the final dispersion. % 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, as the components of the Although the dispersion can tolerate traces of water depending on their degree of purity, it is obvious 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 - in comparison with the other solvents used in the preparation of the dispersion - on the content final water dispersion. According to a particular embodiment of the present invention, the dispersions of silver nanoparticles 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 compounds of formulation / preparation of the dispersion, 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 which is different from the "b" compound (cyclooctane) used and its content in the ink is greater than 10% by weight and less than 80% by weight. weight; the 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 / or or terpinen-4-ol, preferably alpha-terpineol), isoborneol, citronellol, linalool, terminalol, 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 glycols examples of which are 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 example glycol ethers among the mono- or di-ethers of glycols among which we will mention by way of example ethylene glycol propyl ether, ethylene glycol butyl ether, ethylene glycol phenyl ether, propylene glycol phenyl ether, diethylene glycol methyl ether, ethylene 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 glycols 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] / [aliphatic monohydric alcohol ] 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] the 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 cellulosic 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. For example,

 ascorbic acid or vitamin C (E300), sodium ascorbates (E301), calcium (E302), diacetyl 5-6-1 -ascorbic acid (E303), palmityl 6-1 -ascorbic acid (E304); citric acid (E330), sodium citrate (E331), potassium (E332) and calcium citrate (E333);

 tartaric acid (E334), tartrates of sodium (E335), potassium (E336) and sodium and potassium (E337);

 butylhydroxyanisole (E320) and butylhydroxytoluol (E321);

 octyl (E311) or dodecyl (E312) gallates;

 sodium lactate (E325), potassium (E326) or calcium lactate (E327);

 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,

 and 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 below.

 1) in a reactor containing the solution of silver nanoparticles in dispersion (mixture of compounds "a", "b", "c", and "d") is added a mixture of solvent "e" 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 nanoparticle solution dispersed silver (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 solution of silver nanoparticles in dispersion (mixture of compounds "a", "b", "c", and "d") and the whole is stirred for 15 min at room temperature.

 According to one 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% by weight. and 40% by weight.

 According to one embodiment of the present invention, the silver ink comprises

A dispersion according to the present invention (with 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,

 A compound "e" in a content greater than 10% by weight and less than 80% by weight, preferably less than 70% by weight, preferably between 15 and 65% by weight,

 An optional compound "f" (rheology modifying agent) in a content of less than 20% by weight, preferably between 0.1 and 2% by weight,

 An optional compound "g" consisting of an antioxidant agent in a content of less than 10% by weight, preferably less than 3% by weight, and

 An "X" (cyclooctane) compound in a content of less than 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 silver ink comprises the compound "g" consisting of an antioxidant in a content greater than 0.01% 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 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 polyethertetphthalate), 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 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 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 citrate the greatest impact - compared with the other solvents used in the preparation of the ink - on 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 less than 1% by weight. 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:

 at. 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",

vs. 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 the normal or ambient pressure conditions and, with respect to temperature, the latter is generally less than 80 ° C, preferably less than 70 ° C. For example, the Applicant has found that it is preferable to maintain the pressure conditions during the preparation of the dispersion at values oscillating at most 30%, preferably 15% around the values of the normal or ambient pressure conditions. 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:

 at. introduction of 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-based ink according to the present invention is characterized by the following consecutive steps:

 at. 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 stay 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 an ink preparation 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 synthesis of the dispersions and the ink formulations were prepared in accordance with the embodiments described below. 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 advantageously be measured according to the following method:

 An ink deposited by spincoating on a substrate (600 rpm / 3 min - for example glass) is annealed using a hot plate or an oven. An analysis of the square resistance is carried out under the following conditions:

 Device reference: S302 Resistivity Stand

4 point head reference: SP4-40045TFY

 Power Source Reference: Agilent U8001A

 Multimeter reference: Agilent U3400

 Measuring temperature: room temperature

 Coefficient conversion voltage / resistance: 4,5324

 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 according to the present invention were preferably less than 100 mohms / sq for higher thicknesses or equal to 1 μιη (annealing temperature of

150 ° C). This particular property of square strength 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 less

(as demonstrated in the example and the measure).

 The silver nanoparticles 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

 Device: TGA Q50 from TA Instrument

 Crucible: Alumina

 Method: ramp

Measurement 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 may 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 Malvern with the following characteristics:

 DLS (Dynamic light scattering) measurement method:

 - Tank type: optical glass

 - Material: Ag

 - Refractive index of nanoparticles: 0.54

 - Absorption: 0.001

 - Dispersant: Cyclooctane

 - Temperature: 20 ° C

 - Viscosity: 2.133

 - Dispersing refractive index: 1.458

 - General Options: Mark-Houwink parameters

 - Analysis Model: General purpose

 - Equilibration: 120 s

 - Number of measure: 4

 FIGS. 1 and 2 are representative of a general example of DLS (Dynamic light scattering) spectrum obtained during the synthesis of the nanoparticles according to the present invention, respectively with synthetic solvent (FIG. 1) and when the dispersing agent is used as a solvent for synthesis (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

D ₅₀ 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 be advantageously measured according to the following method:

Device: AR-G2 Rheometer by TA Instrument

Conditioning time: Pre-shear at 40 sec ^-1 for 10 seconds / equilibration for 1 minute

 Test Type: Shear Bearings

Bearings: 40 s ^"1 , 100 s ^{" 1} and 1000 s ^"1

 Duration of a stage: 5 minutes

 Mode: linear

Measure: every 10 seconds

 Temperature: 20 ° C

 Method of reprocessing the curve: Newtonian

Retarded Zone: The Whole 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:

 Device: OCA 15 of Appolo Instrument

 Method: Drop hanging

Reprocessing: Laplace-Young

 Volume: 0.2 μΐ,

 Flow rate: 1 μί / β

 Needle diameter: 1.65 mm

Temperature: 20 ° C

Formulations - Table

Alpha hexylene dodecyl

CO Octylamine CO Butanol DEGDBE

 Ex Ag Laminate Terpineol Glycol

 "B" "d" "X" "e" "e"

 "C" "e" "e"

Comp. 20 22.1 2 0.3 30.6 20 5 0 0

Fl 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 Ag = silver nanoparticles (D50: 8.0 nm)

CO = Cyclooctane

 DEGDBE = Diethylene glycol dibutyl ether

The viscosity and surface tension values of the inks are shown in the table below.

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 Fl 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, annealed 150 ° C 30 min). The values are shown in the table below.

Spin-coating deposition tests were also performed for these three inks. A visual representation is given in Figure 4. The spin-coating deposits are better quality for examples Fl and F2 (more homogeneous deposit, brighter, mirror effect) than for the comparative example.

Claims

1. Ink based on silver nanoparticles whose composition includes  A. a dispersion of silver nanoparticles in a content of between 5 and 60% by weight, said dispersion comprising  at. a compound "a" consisting of silver nanoparticles,  b. a compound "b" consisting of a cyclooctane solvent,  vs. 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 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. a compound "X" 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  o 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. 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 and 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.  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 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. Ink according to 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; , alpha-terpineol), isoborneol, citronellol, linalool, borneol, geraniol, and / or a mixture of two or more of said alcohols, the aliphatic monohydric alcohol (compound "e") is divided into the group consisting of ethanol, propanol, butanol, pentanol and hexanol and their isomers and / or a mixture of two or more of said alcohols, the glycol is selected from 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 of two or more of said glycols, and glycol ether (compound "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 their mixtures. 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 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. 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. 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. 13. 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 P / o by weight, for example less than 0.5% by weight, or even less than 0.2% by weight. 14. 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.