Ink erasing fluid and kits containing same

Abstract

The present invention relates to a kit comprising: a) an aqueous writing ink composition containing, as a colorant, metallic nanoparticles, the metallic nanoparticles essentially consisting of a metal, the metal being selected from silver, gold, aluminum and / or copper, and a dispersant; and b) an eraser fluid containing at least one oxidizing agent. The present invention also relates to an aqueous eraser fluid for erasing an aqueous writing ink composition containing metallic nanoparticles as a colorant, the aqueous eraser fluid containing: - an oxidizing agent; and - a volatile solvent. The present invention further relates to a writing instrument containing the eraser fluid, to the use of the eraser fluid and / or the kit containing it, as well as to a method for correcting errors in a writing mark on a porous substrate.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of European Patent Application No. 21305223.6, entitled "NK ERADICATING FLUID AND KIT CONTAINING IT," filed on February 25, 2021, the contents of which are incorporated herein by reference.

[0002] FIELD OF THEINVENTION The present invention relates to ink erasing fluids, erasable inks, and kits containing same.

[0003] The three techniques are used to correct errors in the written marks once applied onto the porous substrate. - An ink eraser system (pH ink) comprising an erasable ink (with at least one pH-sensitive dye as a colorant), an erasing fluid (pH eraser), and a rewrite ink (with at least one non-pH-sensitive dye).

[0004] One problem associated with this ink eraser system is that three different writing instruments may be required, one for the erasing fluid, one for the erasable ink, and one for the rewrite ink, which may not be convenient for the user. Additionally, consumers may easily confuse the erasable ink, which is to be used for the original marking, with the rewrite ink. - Thermochromic inks (with leuco dyes as colorants) that can be erased using the heat generated by rubbing with an eraser.

[0005] A technical problem with thermochromic inks is that erasure is reversible at low temperatures, so erased lines can be unwantedly recreated. - Peelable inks (with pigments as colorants) that can be removed with the use of an eraser.

[0006] A technical problem with peelable ink is that it can change the texture of a porous surface after erasure, drawing the reader's attention to the error that has been corrected.

[0007] Therefore, there is a need to find new aqueous erasable ink compositions that preferably have good erasability while avoiding undesirable color loss due to temperature changes and / or undesirable color return.In addition, it would be advantageous to find an improved system in which only two fluids are needed, namely, an erasing fluid and a single ink that can be corrected using the erasing fluid, can also be used to make corrections, or can be used in place of another overwrite ink.

[0008] To overcome these technical problems, the inventors have surprisingly found that the use of metal nanoparticles as colorants in an aqueous ink composition, where the metal nanoparticles consist essentially of metals, the metals being selected from silver, gold, aluminum, and / or copper, such as homopolymers or copolymers of vinylpyrrolidone and / or homopolymers or copolymers of vinyl alcohol, and mixtures thereof, can be easily erased by an oxidizing agent, and the same ink can be used as an overwrite ink. Furthermore, without being bound by theory, the use of a dispersing agent, such as polyvinylpyrrolidone and / or polyvinyl alcohol, in an aqueous ink composition containing metal nanoparticles as colorants provides excellent steric stability and / or helps prevent the metal nanoparticles from coming into direct contact and / or agglomerating and / or precipitating in the aqueous ink, thereby allowing a more robust and / or stable plasmonic effect to be obtained. In particular, such agglomeration and / or aggregation and / or precipitating may prevent the attainment of the plasmonic effect. Furthermore, the presence of a dispersing agent may allow the ink to be more easily erased with an oxidizing agent.

[0009] US Patent No. 5,427,278 describes the use of oxidizing agents to remove transparent or translucent highlighting inks. However, such inks do not contain metal nanoparticles as colorants. Furthermore, the list of oxidizing agents that can be used as erasers is short, such as halogen-containing bleaching solutions; alkali and alkaline earth salt solutions formed with hypochlorite (bleaching agent), triazine chlorine, and triazine-type derivatives; sodium, lithium, and calcium hypochlorite solutions; chlorophosphorus triazinetrione solutions, such as sodium or potassium dichloro-s-triazinetrione and trichloro-striazinetrione solutions; sodium, potassium, and ammonium persulfate, and potassium monopersulfate solutions; and solutions of 1-bromo-3-chloro-5-dimethylhydantoin alone or in combination with 1,3-dichloro-5,5-dimethylhydantoin. In particular, the document notes that a 3% solution of hydrogen peroxide, a 6% solution of hydrogen peroxide, and a 6% solution of hydrogen peroxide with added ammonia (a hair bleach) were ineffective, and further notes that tests with various solutions of nitrates of yttrium, strontium, sodium, barium, potassium, cerium, silver, cobalt, ammonium cerium, and lanthanum, as well as tests with perchloric acid, dichromate, and potassium permanganate also proved unsatisfactory. Thus, only certain oxidizing agents could be used as scavenging agents.

[0010] EP 2180022 discloses erasing fluids and erasable inks. However, such inks do not contain metal nanoparticles as colorants. Furthermore, oxidizing agents are cited in a long list of erasing agents, and no specific examples are given.

[0011] WO 2020 / 104367 and WO 2020 / 104346 disclose aqueous writing ink compositions containing metal nanoparticles as colorants. However, these documents do not disclose the presence of a dispersant added to the aqueous ink, nor the possibility of using an eraser fluid containing an oxidizing agent to erase the writing marks.

[0012] Thus, there is a need for a kit that includes a specific erasing fluid and a specific erasable ink, particularly one that can also be used as an overwrite ink.

[0013] Thus, the present invention provides a) an aqueous writing ink composition, more specifically an aqueous gel ink; - metallic nanoparticles as colorants, more particularly as the only colorants, which consist essentially of a metal, the metal being selected from silver, gold, aluminum and / or copper, more particularly the metal being silver, and an aqueous writing ink composition containing a dispersant, such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and mixtures thereof; b) an eliminator fluid containing at least one oxidizing agent, and more particularly a kit consisting of the above.

[0014] The present invention will now be described in detail, with specific embodiments being provided to better illustrate the present invention, but it should be understood that the present invention is not limited to these specific embodiments.

[0015] In the context of the present invention, "comprising a" and "containing a" should be understood to be synonymous with "comprising at least one" and "containing at least one."

[0016] In the context of the present invention, the expressions "between ... and ..." or "in the range from ... to ..." are to be understood as including the limits.

[0017] In the sense of the present invention, the term "ink" is intended to mean a "writing ink" intended to be used in a writing instrument, in particular in a pen. Writing inks should not be confused with "printing inks" that are used in printing presses and do not have the same technical constraints and therefore the same specifications. In fact, writing inks must not contain solid particles of a size larger than the channels of the writing instrument, in order to avoid clogging of the writing instrument, which would inevitably result in an irreversible halt to writing. Furthermore, they must allow an ink flow rate suitable for the writing instrument used, in particular a writing flow rate of 100 to 500 mg / 200 m, in particular a writing flow rate of 150 to 400 mg / 200 m. They must also dry sufficiently quickly to avoid soiling the writing medium. They must also avoid problems of migration (bleed-through) over time. An ink according to the invention will therefore be suitable for the writing instrument for which it is intended, in particular a pen.

[0018] Furthermore, the "writing ink" must not be too fluid to avoid leakage during writing, but must be sufficiently fluid to facilitate the flow of the writing action.

[0019] In the particular case of the present invention, the writing ink may more specifically be a "gel ink". In particular, such a gel ink corresponds to a thixotropic ink, in particular at 20° C. and at rest (1s -1 The viscosity measured at a shear rate of 5,000 s at 20 °C using the same rheometer, for example a cone and plate rheometer such as a Malvern KINEXUS with a 60 mm cone and 1° angle. -1 In certain embodiments, the viscosity of the gel ink measured under these conditions is different from, and in particular higher than, the viscosity measured at a shear rate of 1s. -1 At a shear rate of 1,000 to 7,000 mPa.s, specifically, 2,000 to 5,000 mPa.s, more specifically, 2,500 to 3,500 mPa.s, 5,000 to 6,000 mPa.s, -1Specifically, the shear rate is in the range of 5 to 50 mPa.s, more specifically, 7 to 40 mPa.s, and even more specifically, 10 to 20 mPa.s.

[0020] In the sense of the present invention, the term "metal nanoparticles essentially consisting of metal" is intended to mean that the main component of the nanoparticles is metal, with other components in the metal nanoparticles, in particular impurities such as metal oxides (silver oxide, gold oxide, copper oxide, aluminum oxide), being present only in trace amounts. More specifically, the content of metal is at least 95% by weight, even more specifically at least 98% by weight, relative to the total weight of the nanoparticles. More specifically, the content of impurities is less than 5% by weight, even more specifically less than 2% by weight, relative to the total weight of the nanoparticles.

[0021] In certain embodiments, the metal nanoparticles consist solely of metal.

[0022] More specifically, the metal of the metal nanoparticles according to the invention comprises at least silver, gold, and mixtures thereof, even more specifically at least silver, even more specifically essentially consisting thereof, in particular consisting thereof. Even more specifically, the metal nanoparticles are silver nanoparticles, gold nanoparticles, or mixtures thereof. Even more specifically, the metal nanoparticles are silver nanoparticles.

[0023] According to a particular embodiment, the aqueous writing ink composition is essentially free of iron, in particular iron powder.

[0024] More specifically, the metal nanoparticles according to the invention have an average particle size in the range of 1-200 nm, even more specifically, 2-100 nm, even more specifically, 5-100 nm. More specifically, the longest dimension of the metal nanoparticles is in the range of 1-200 nm, even more specifically, 2-100 nm, even more specifically, 5-100 nm. More specifically, all dimensions of the metal nanoparticles are in the range of 1-200 nm, even more specifically, 2-100 nm, even more specifically, 5-100 nm. This average particle size and particle dimensions are determined by analysis of 2D images (microscope: JEOL ARM 200) according to the ISO 9001:2015 standard.

[0025] The metal nanoparticles according to the invention can have different shapes, such as spheres, platelets, rods, wires (especially pentagonal, Y-shaped, K-shaped and multi-branched wires), bars, faceted quasi-spherical shapes, prisms, flowers, polyhedral shapes, triangular shapes, bipyramidal shapes, truncated triangular shapes, square shapes, rectangular shapes, hexagonal plates, sea urchin shapes or even more irregular shapes, more particularly sea urchin shapes and / or polyhedral shapes, more advantageously not spherical.

[0026] In certain embodiments, the total amount of metal nanoparticles in the aqueous writing ink composition (a) is in the range of 0.01 to 10 wt %, specifically 0.01 to 5 wt %, and more specifically 0.1 to 5 wt %, based on the total weight of the aqueous writing ink composition (a).

[0027] The metal nanoparticles according to the present invention act as a colorant in the aqueous writing ink composition (a).

[0028] In certain embodiments, the aqueous writing ink composition (a) containing metal nanoparticles exhibits a plasmonic effect (also called plasmonic effect). Thus, depending on the content of the components used, different plasmonic colors of the ink composition can be obtained.

[0029] In fact, the plasmonic color is due to both the light absorption by the metal nanoparticles and / or the spacing of the metal nanoparticles in the aqueous writing ink composition (a).

[0030] The color of the aqueous writing ink compositions (or the materials in which they are included) along with their properties can vary depending on their size, shape, and distance due to plasmon resonance, which is frequently present in the case of metal nanoparticles.

[0031] When metal nanoparticles are exposed to waves of a particular frequency, electrons congregate in specific locations that vary depending on the shape and size of the metal nanoparticle. This agglomeration of electrons can create anisotropy in the metal nanoparticles, which in turn leads to changes in the absorption and scattering of light, resulting in a particular color.

[0032] Plasmon resonance can also be affected by the distance between the metal nanoparticles due to their bonding: indeed, the closer the metal nanoparticles are, the more they interact with each other, increasing their bonding effect, also called the plasmonic effect.

[0033] Similarly, the shape of the metal nanoparticles affects the plasmon resonance.

[0034] In particular, such plasmonic effects can be characterized by UV (ultraviolet)-visible-NIR (near infrared) absorption spectroscopy.

[0035] Specifically, the total amount of the aqueous writing ink is in the range of 50 to 95% by weight, more specifically, 60 to 90% by weight, and even more specifically, 70 to 85% by weight, based on the total weight of the aqueous ink composition.

[0036] The aqueous writing ink (a) contains a dispersant (also called a stabilizer), such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and mixtures thereof, more particularly a homopolymer and / or copolymer of vinylpyrrolidone, and even more particularly polyvinylpyrrolidone (PVP).

[0037] More specifically, the homopolymer and / or copolymer(s) of vinylpyrrolidone, in particular the homopolymer, may have a weight average molecular weight of more than 5 kDa, in particular from 15 to 2000 kDa, more specifically from 30 to 500 kDa, even more specifically from 80 to 350 kDa, e.g. PVP K40.

[0038] More specifically, the homopolymer and / or copolymer(s) of vinyl alcohol, especially the homopolymer, may have a weight average molecular weight of more than 20 kDa, specifically, 50-100 kDa, more specifically, 60-80 kDa.

[0039] Without being bound by theory, the dispersant may in particular avoid agglomeration and / or aggregation and / or sedimentation of the metal nanoparticles, which may prevent the formation of the plasmonic effect, in particular making such writing inks more difficult to erase with an eraser fluid containing an oxidizer, since such agglomeration and / or aggregation and / or sedimentation may prevent the acquisition of the plasmonic effect.

[0040] More specifically, the total amount of the dispersant is in the range of 0.01 to 10% by weight, more specifically 0.01 to 5% by weight, and even more specifically 0.1 to 0.4% by weight, based on the total weight of the aqueous writing ink composition (a).

[0041] The aqueous writing ink composition (a) comprises reducing agents, more particularly selected from alkali metal or alkaline earth metal salts, and / or hydroxylamine (NHOH), and / or ascorbic acid, and / or oxalic acid, and / or formic acid, and / or formaldehyde, and / or hydrazine, and / or substituted hydrazines, such as 1,1-dimethylhydrazine or 1,2-dimethylhydrazine, and / or sodium hydrosulfite, and / or tributylstannane, and / or tributyltin hydride, and / or triphenylphosphine, and / or triphenylphosphite, and / or trichlorosilane, and / or triethylsilane, tris(trimethylsilyl)silane, and / or polymethylhydroxysilane, and / or esters of retinol of formula (I)

[0042] [ka] wherein R is an optionally substituted C1-C6 aliphatic group, more particularly a (C1-C6) alkyl group, and / or citric acid and / or a derivative of citric acid selected from esters, amides and thioesters of citric acid, salts of citric acid or of said derivatives, solvates of citric acid or of said derivatives, such as, for example, hydrates, and mixtures thereof, and / or N-acyl-aminophenols, the hydroxyl group being preferably in the meta or para position of the benzene group, preferably in the para position, preferably N-acyl-aminophenols of formula HO-R1-NH-CO-R2, wherein R1 is a benzene ring and R2 is an alkyl group preferably containing 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and preferably the hydroxyl group being in the meta or para position, preferably in the para position, and / or It may further contain an alkali metal hydride, in particular sodium borohydride NaBH4.

[0043] Specifically, in the retinol ester(s) of formula (I), R represents a C1-C6 aliphatic group, which is optionally substituted with at least one hydroxyl, halogen, amino, C1-C3 alkyl, and / or C1-C3 alkoxy group, more specifically a C1-C6 alkyl group, even more specifically a C1-C4 alkyl group, in particular a methyl group, and in particular unsubstituted. The retinol ester represented by formula (I) in which R represents a methyl group is commonly known as retinyl acetate (CAS number: 127-47-9), also known as vitamin A acetate, and can be purchased from Sigma-Aldrich.

[0044] Specifically, the N-acyl-aminophenol is N-acetyl-para-aminophenol. According to this particular embodiment, in the formula HO-R1-NH-CO-R2, R1 is a benzene ring, R2 is a methyl radical and the hydroxyl group is in the para position. N-acetyl-para-aminophenol (CAS number: 103-90-2), also known as paracetamol or acetaminophen, can be purchased under different trade names such as Doliprane®, Tylenol®, Calpol®, Panadol®, Dafalgan®, Efferalgan®, etc.

[0045] More specifically, the reducing agent of the aqueous writing ink composition (a) is - alkali metal citrates and / or chlorides and / or alkaline earth metal salts and / or carbonates, more particularly alkali citrates and / or alkali chlorides and / or alkali carbonates, even more particularly sodium citrate and / or magnesium chloride and / or calcium chloride, even more particularly sodium citrate; -Ascorbic acid; -Alkali metal hydrides, specifically sodium borohydride NaBH4; - and mixtures thereof.

[0046] More specifically, the reducing agent is a mixture of sodium citrate (particularly trisodium citrate), ascorbic acid, and sodium borohydride NaBH4.

[0047] In the present invention, the alkali metal of the citrate may be selected from lithium citrate, sodium citrate, potassium citrate, rubidium citrate, cesium citrate, and francium citrate, specifically sodium citrate or potassium citrate, more specifically sodium citrate.

[0048] In the present invention, the alkaline earth metal salt of citrate may be selected from beryllium citrate, magnesium citrate, calcium citrate, strontium citrate, barium citrate, and radium citrate, specifically magnesium citrate, or calcium citrate, more specifically calcium citrate.

[0049] In one embodiment of the present invention, the alkali metal or alkaline earth metal carbonate may be selected from potassium carbonate, sodium carbonate, magnesium carbonate, calcium carbonate, strontium carbonate, barium carbonate, and mixtures thereof, more specifically at least one of magnesium carbonate, calcium carbonate, strontium carbonate, and barium carbonate, and even more specifically calcium carbonate.

[0050] In the present invention, the alkali metal hydride is sodium borohydride (NaBH4), sodium cyanoborohydride (NaBH3CN )、The alkali metal hydride may be selected from sodium triacetoxyborohydride (NaHB(OAc)3), sodium tri-sec-butylborohydride, potassium tri-sec-butylborohydride, potassium triethylborohydride, lithium triethylborohydride, lithium tri-sec-butylborohydride, nickel borohydride, lithium aluminate hydride, diisobutylaluminium hydride, sodium bis(2-methoxyethoxyaluminium hydride), and in particular the alkali metal hydride is sodium borohydride (NaBH4).

[0051] In particular, if present, the total amount of alkali metal salts in the aqueous writing ink composition (a) is at least 0.001% by weight, and in particular in the range of 0.01 to 0.05% by weight, based on the total weight of the aqueous writing ink composition (a).

[0052] In particular, if present, the amount of alkali metal hydride in the aqueous writing ink composition (a) is at least 0.0000001 wt. %, and more particularly in the range of 0.0000001 to 0.00007 wt. %, based on the total weight of the aqueous writing ink composition (a).

[0053] In the present invention, the derivatives of citric acid are selected from esters, amides, and thioesters of citric acid, salts of citric acid or its derivatives, solvates of citric acid or its derivatives, such as hydrates, and mixtures thereof. Suppliers of citric acid and / or its derivatives are selected from Fluka™, Sigma-Aldrich™, TCI chemicals™.

[0054] The ester of citric acid is specifically an alkyl ester, preferably a C1-30 alkyl ester, preferably a C1-20 alkyl ester, preferably a C1-6 alkyl ester. The ester of citric acid can be a monoester, a diester and / or a triester, preferably a triester of citric acid. The ester of citric acid used in the present invention is selected from the group consisting of tri-C citric acid, such as isodecyl citrate, isopropyl citrate, stearyl citrate, dilauryl citrate, distearyl citrate, tributyl citrate, tricaprylyl citrate, triethyl citrate, triethylhexyl citrate, trihexyldecyl citrate, triisocetyl citrate, trilauryl citrate, trioctyldodecyl citrate, trioleyl citrate, triisostearyl citrate, tristearyl citrate, ethyl citrate, tributyl citrate or triethyl citrate. 12-15 -alkyl, tricaprylyl citrate, triethylhexyl citrate, triisocetyl citrate, trioctyldodecyl citrate, triisostearyl citrate, isodecyl citrate, stearyl citrate, dilauryl citrate, and ethyl citrate.Preferably, the esters of citric acid of the present invention are tributyl citrate and triethyl citrate.

[0055] The amides of citric acid used in the present invention can be prepared by the reaction of a primary amine with citric acid. The amination reaction to form amides is described in the Kirk-Othmer Encyclopedia of Chemical Technology, 4 thThe reaction can be carried out using a variety of conditions well known in the organic chemistry art, as described in Ed., Vol.2, p.348-351. A preferred method involves reacting citric acid with three or more equivalents in a protic solvent. Any primary amine or mixture of primary amines preferably containing the requisite C1-C18 alkyl substituents can be utilized in the preparation of the trialkylcitramids of the present invention. The alkyl groups in the citramide can be the same or different and can be linear or branched. Examples of suitable alkyl groups are methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, n-pentyl, 2-pentyl, 3-pentyl, iso-pentyl, neopentyl, cyclopentyl, 2-methylbutyl, 3-methyl-2-butyl, n-hexyl, 2-hexyl, 3-hexyl, cyclohexyl, 2-ethylbutyl, 4-methyl-2-pentyl, n-heptyl, n-octyl, n-2-ethylhexyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl.Specifically, the amides of citric acid of the present invention are tributylcitramide and triethylcitramide.

[0056] The thioester of citric acid used in the present invention can be prepared by the reaction of thiol with a derivative of citric acid. Some examples of thiol and derivatives that can be used include allyl mercaptan, 2-aminoethanethiol, 2-aminobenzenethiol, 3-aminobenzenethiol, 4-aminobenzenethiol, 1,3-benzenedimethanethiol, and 1,4-benzenedimethanethiol. Specifically, the thioester of citric acid can be obtained by the reaction between allyl mercaptan and citric acid.

[0057] Salts of citric acid, also known as citrates, may involve various levels (mono, di, tri) of different metal cations such as calcium, potassium, or sodium. Citric acid is present in more than trace amounts in various fruits and vegetables, especially citrus fruits. All citrates are produced by the chemical reaction of citric acid with the hydroxide or carbonate of the respective salt.

[0058] The salts of citric acid used in the present invention include aluminum citrate, calcium citrate, copper citrate, diammonium citrate, disodium citrate, cupric citrate, ferric citrate, magnesium citrate, manganese citrate, monosodium citrate, potassium citrate, sodium citrate, zinc citrate. Specifically, the salts of citric acid used in the present invention are sodium citrate, potassium citrate, and diammonium citrate.

[0059] The solvate of citric acid or its derivative in the present invention is selected from citric acid monohydrate, trisodium citrate dihydrate, and disodium citrate trihydrate. Specifically, the solvate of citric acid in the present invention is citric acid monohydrate.

[0060] In certain embodiments, the amount of reducing agent in the aqueous writing ink composition (a) ranges from 0.0000001% to 0.5% by weight, based on the total weight of the aqueous writing ink composition (a).

[0061] In a specific embodiment, the aqueous writing ink composition (a) contains sodium citrate in a total amount, based on the total weight of the aqueous writing ink composition (a), specifically in the range of 0.001 to 0.1 wt %, more specifically in the range of 0.01 to 0.05 wt %.

[0062] In a specific embodiment, the aqueous writing ink composition (a) contains ascorbic acid in a total amount in the range of specifically 0.0005 to 0.5 wt %, more specifically 0.001 to 0.1 wt %, and even more specifically 0.005 to 0.05 wt %, based on the total weight of the aqueous writing ink composition (a).

[0063] In certain embodiments, the aqueous writing ink composition (a) contains sodium borohydride in a total amount of at least 0.0000001% by weight, more specifically in the range of 0.0000001 to 0.00007% by weight, based on the total weight of the aqueous writing ink composition (a).

[0064] The water-based writing ink (a) may also contain classical ink ingredients, in particular classical gel ink ingredients such as co-solvents, antimicrobial agents, corrosion inhibitors, antifoam agents, rheology modifiers, etc., as described below.

[0065] The aqueous writing ink (a) may therefore contain a co-solvent. Among the co-solvents that can be used are the following: - glycol ethers such as triethylene glycol, polyethylene glycol, diethylene glycol monoethyl ether, diethylene-glycol-monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, phenoxyethanol, phenoxypropanol, etc. -Alcohols, such as benzyl alcohol, glycerin, diglycerin, polyglycerin, etc. 15 a linear or branched alcohol of esters such as ethyl acetate or propyl acetate, Carbonate esters, such as propylene carbonate or ethylene carbonate, - mention may be made of polar solvents that are miscible in water, such as mixtures thereof.

[0066] In certain embodiments, the co-solvent is selected from the group consisting of glycol ethers, more specifically, triethylene glycol, polyethylene glycol, diethylene glycol monoethyl ether, diethylene-glycol-monobutyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monomethyl ether, phenoxyethanol, phenoxypropanol, and mixtures thereof, and in even more specific embodiments, the co-solvent is selected from the group consisting of triethylene glycol, polyethylene glycol, and mixtures thereof.

[0067] Specifically, the total amount of co-solvents in the aqueous writing ink (a) is in the range of 5 to 35% by weight, more specifically 9 to 30% by weight, and even more specifically 11 to 25% by weight, based on the total weight of the aqueous writing ink (a).

[0068] The aqueous writing ink (a) may contain an antimicrobial agent selected from the group consisting of isothiazolinones (ACTICIDE® from Thor), specifically 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and mixtures thereof.

[0069] Specifically, the total amount of the antibacterial agent in the water-based writing ink (a) is in the range of 0.01 to 0.5% by weight, more specifically, 0.1 to 0.2% by weight, based on the total weight of the water-based writing ink (a).

[0070] The water-based writing ink (a) may contain a corrosion inhibitor, in particular a corrosion inhibitor selected from the group consisting of tolytriazole, benzotriazole, and mixtures thereof.

[0071] Specifically, the total amount of the corrosion inhibitor in the water-based writing ink (a) is in the range of 0.05 to 1 wt %, more specifically, 0.07 to 0.6 wt %, and even more specifically, 0.08 to 0.4 wt %, based on the total weight of the water-based writing ink (a).

[0072] The aqueous writing ink (a) may contain an antifoaming agent, in particular a polysiloxane-based antifoaming agent, more particularly an aqueous emulsion of modified polysiloxane (such as MOUSSEX® from Synthron, TEGO® Foamex from Evonik, etc.).

[0073] Specifically, the total amount of the defoaming agent in the aqueous writing ink (a) is in the range of 0.05 to 1 wt %, more specifically, 0.1 to 0.5 wt %, and even more specifically, 0.2 to 0.4 wt %, based on the total weight of the aqueous writing ink.

[0074] The aqueous writing ink (a) may also comprise a rheology modifier capable of producing a gelling effect, in particular a thixotropic phenomenon in which the viscosity is dependent on the shear rate in time, selected from the group consisting of polysaccharides such as, for example, xanthan gum, gum arabic and mixtures thereof.

[0075] Specifically, the total amount of rheology modifier in the aqueous writing ink (a) is in the range of 0.08 to 2 wt. %, more specifically, 0.2 to 0.8 wt. %, and even more specifically, 0.3 to 0.6 wt. %, based on the total weight of the aqueous writing ink (a).

[0076] The water-based writing ink (a) also comprises - pH adjusters such as sodium hydroxide and triethanolamine, -lubricants, -coalescents, crosslinking agent, wetting agents, -plasticizers, -Antioxidants, and -Other additives such as UV stabilizers may also be included.

[0077] In a particular embodiment, the water-based writing ink according to the present invention does not contain any other colorant than the metal nanoparticles, and therefore does not contain any dye or pigment, in which case the color of the water-based writing ink (a) is due only to the metal nanoparticles, and the ink is an erasable water-based writing ink.

[0078] For the purposes of the present invention, the term "erasable ink" is intended to mean any ink that can be erased after writing by using the eraser fluid (b) according to the present invention. Thus, a written mark obtained with this ink, in particular on a porous support, can be erased at any time after writing by using the eraser fluid (b) according to the present invention.

[0079] Specifically, the ink is an irreversibly erasable water-based writing ink: the ink color cannot reappear after erasure.

[0080] In another particular embodiment, the water-based writing ink (a) according to the invention contains a further colorant other than the metal nanoparticles, in which case the water-based ink composition is a color-changing ink.

[0081] For the purposes of the present invention, the term "color-changing ink" is intended to mean any ink whose color (first or initial color) can be changed after writing to another color (second color), advantageously different from the first color, by the use of the eraser fluid (b) according to the invention. Thus, the color of the written mark obtained with this ink, in particular on a porous support, can be changed to another color at any time after writing by the use of the eraser fluid (b) according to the invention.

[0082] In particular, the ink is an irreversible color-changing water-based writing ink: once the color has changed, it is not possible to change it again, in particular to return to the initial color (first color).

[0083] In particular, the further colorant may be a dye, a pigment, or a mixture thereof, in particular a dye.

[0084] The dye or pigment may be any dye or pigment known to a person skilled in the art and may be used in the aqueous writing ink, in particular in the aqueous writing gel ink. Specifically, the total amount of the further colorant in the aqueous writing ink (a) ranges from 0.01 to 30% by weight, more specifically from 0.05 to 25% by weight, based on the total weight of the aqueous writing ink (a).

[0085] In certain embodiments, the colorant is a dye.

[0086] The term "dyes" should be understood to mean any form of colored mineral or organic particles that are soluble in the medium in which they are solubilized, i.e. the aqueous medium of the aqueous writing ink (a) and are intended to color the ink composition applied onto the porous substrate after the ink has been erased by the eraser fluid (b). The presence of dyes in the aqueous writing ink composition (a) allows the initial color of the writing to be changed to another color by erasure in the eraser fluid (b). Advantageously, the dyes are not thermochromic or photochromic or pressure-sensitive dyes.

[0087] Thus, the aqueous writing ink composition (a) according to the present invention comprises at least one dye. The aqueous writing ink composition (a) may also comprise several dyes. The dyes may be, for example, direct dyes (e.g., CI Direct Black 17, 19, 22, 32, 38, 51, 71; CI Direct Yellow 4, 26, 44, 50; CI Direct Red 1, 4, 23, 31, 37, 39, 75, 80, 81, 83, 225, 226, 227; CI Direct Blue 1, 15, 41, 71, 86, 87, 106, 108, 199, etc.), acid dyes, e ... Dyes (e.g., CI Acid Black 1, 2, 24, 26, 31, 52, 107, 109, 110, 119, 154; CI Acid Yellow 1, 7, 17, 19, 23, 25, 29, 38, 42, 49, 61, 72, 78, 110, 127, 135, 141, 142; CI Acid Red 8, 9, 14, 18, 26, 27, 33, 35, 37, 51, 52, 57, 8 2, 83, 87, 92, 94, 111, 129, 131, 138, 186, 249, 254, 265, 276;CI Acid Violet 15, 17, 49;CI Acid Blue 1, 3, 7, 9, 15, 22, 23, 25, 40, 41, 43, 62, 78, 83, 90, 93, 100, 103, 104, 112, 113, 158;CI Acid Green 3, 9, 16 , 25, 27; CI Acid Orange 56, etc.), food dyes (e.g., CI Food Yellow 3, etc.), Malachite Green (C.I 4200), Victoria Blue FB (CI 44045) Methyl Violet FN (CI 42535), Rhodamine F4G (CI 45160), and Rhodamine 6GCP (C.I 45160), and mixtures thereof.

[0088] If present, the total amount of dyes in the aqueous writing ink (a) may range from 0.01 to 30% by weight, advantageously from 0.05 to 25% by weight, more advantageously from 0.3 to 10% by weight, based on the total weight of the aqueous writing ink composition (a).

[0089] In another particular embodiment, the colorant is a pigment.

[0090] The term "pigments" should be understood to mean any form of white or colored mineral or organic particles, except metal nanoparticles, that are insoluble in the medium in which they are solubilized, i.e. the aqueous medium of the aqueous writing ink composition (a), and that are intended to color the ink composition when applied onto a porous substrate after the ink has been erased by the eraser fluid (b). Thus, pigments may include, for example, inorganic pigments such as carbon black, ultramarine, titanium dioxide pigments, organic pigments such as azo pigments, phthalocyanine pigments, indigo pigments, thioindigo pigments, threne pigments, quinacridone pigments, anthraquinone pigments, thoron pigments, diketopyrrolopyrrole pigments, dioxazine pigments, perylene pigments, perinone pigments, isoindolinone pigments, fluorescent pigments, phosphorescent pigments, pearlescent pigments, synthetic mica, glass flakes, alumina, transparent coatings of metal oxides such as titanium oxide, etc. Pigments are also generally contained in dispersions, which are milled or reduced in particle size with suitable dispersants to achieve stable dispersion.Pigments are specifically pigment dispersions, more specifically selected from the group consisting of Pigment Black 7 (such as Flexiverse III black 7 by SunChemical), Pigment Blue 15:3 (such as APE FRE BL 15:3 DISP by SunChemical), Pigment Red (such as Pigment red 210 by SunChemical), Pigment Green 7 (such as Sunsperse Eco green, Flexiverse FD Green, Flexiverse Green 7, Flexiverse HC GRN 7 by SunChemical), Pigment Violet 23 (such as Cellusperse A Violet 4 BP by SunChemical), Pigment Yellow 74 (such as FG Yellow 1SL by SunChemical), and mixtures thereof.In certain embodiments, the pigment is selected from the group consisting of Pigment Black 7 (such as Flexiverse III black 7 by SunChemical®), Pigment Blue 15:3 (such as APE FRE BL 15:3 DISP by SunChemical®), and mixtures thereof.

[0091] According to a particular embodiment, the diameter of the pigment in the pigment dispersion is less than 1 μm, preferably less than 0.7 μm.

[0092] Specifically, the total amount of the pigment dispersion in the aqueous writing ink (a) is in the range of 0.1 to 30% by weight, more specifically, 0.05 to 25% by weight, and even more specifically, 0.3 to 10% by weight, based on the total weight of the aqueous writing ink composition (a).

[0093] Specifically, the total amount of pigment in the pigment dispersion is in the range of 10 to 50% by weight, more specifically, 30 to 50% by weight, even more specifically, 35 to 45% by weight, and even more specifically, 38 to 45% by weight, based on the total weight of the pigment dispersion.

[0094] In certain embodiments, the water-based writing ink (a) has a fixed color.

[0095] In the sense of the present invention, the term "fixed color" is intended to mean that the color of the aqueous gel ink by visual observation is the same, in particular within 7 calendar days (1 week), and therefore before application of the eraser fluid (b), before application on an absorbent support of paper, cardboard, or textile, and after application on the absorbent support. In another particular embodiment, the aqueous writing ink (a) does not have a variable color.

[0096] In the sense of the present invention, the term "variable color" is intended to mean that the color of the aqueous gel ink by visual observation is not the same, in particular before the use of the eraser fluid (b), before application onto an absorbent support of paper, cardboard or textile, and after application onto the absorbent support.

[0097] For purposes of the present invention, the term "porous substrate" is intended to mean a substrate that contains pores. A porous substrate has empty spaces or pores that allow an external substance, such as ink, to penetrate into the substrate.

[0098] In particular, the porous substrate is chosen from among porous substrates comprising cellulose fibers, such as paper, printing paper or cardboard.

[0099] The metal nanoparticles according to the present invention can be prepared ex-situ in the form of an aqueous suspension which is added to the rest of the ink ingredients during the preparation of the aqueous writing ink composition (a).

[0100] The metal nanoparticles according to the present invention are generally prepared by reduction of a metal salt with a reducing agent, in particular with two reducing agents, more particularly with three reducing agents, in particular with a strong reducing agent, in particular with an alkali metal or alkaline earth metal salt of citric acid, in particular with an alkali citrate, and more particularly with sodium citrate, an alkali metal hydride, in particular with NaBH4, and ascorbic acid, in the presence of a dispersing agent, such as those mentioned above, such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and more particularly with polyvinylpyrrolidone, in order to control the growth of the nanoparticles and thus their size and shape.

[0101] In a particular embodiment, the process for preparing an aqueous suspension containing metal nanoparticles according to the present invention comprises the steps of: i. preparing an aqueous suspension of metal nanoparticle seeds; ii. Carrying out the growth of metal nanoparticles; iii. Optionally comprising a step of concentrating the metal nanoparticles, in particular by centrifugation of the aqueous suspension obtained in step (ii) and / or evaporation under vacuum and / or tangential flow nanofiltration.

[0102] Step (i) is in particular carried out by mixing a metal salt (silver, gold, aluminium and / or copper salt, in particular a silver and / or gold salt, more particularly a silver salt) with water and a reducing agent, in particular two reducing agents, in particular those mentioned above, in particular an alkali metal or alkaline earth metal salt of citric acid, in particular an alkali citrate, more particularly sodium citrate such as trisodium citrate, and an alkali metal hydride, in particular NaBH4, even more particularly a mixture of sodium citrate and NaBH4.

[0103] In certain embodiments, the total amount of metal salts (silver, gold, aluminum and / or copper salts, specifically silver and / or gold salts, more specifically silver salts) added to the aqueous suspension is in the range of 0.0005-0.05 wt %, more specifically 0.001-0.01 wt %, based on the total weight of the aqueous suspension of metal nanoparticle seeds.

[0104] In certain embodiments, the total amount of alkali metal or alkaline earth metal salt of citric acid, specifically alkali citrate, more specifically sodium citrate such as trisodium citrate, in the aqueous suspension is in the range of 0.0005-0.05 wt %, more specifically 0.001-0.01 wt %, based on the total weight of the aqueous suspension of metal nanoparticle seeds.

[0105] In certain embodiments, the total amount of alkali metal hydride, specifically NaBH4, in the aqueous suspension is in the range of 0.0001-0.01 wt. %, more specifically 0.0005-0.005 wt. %, based on the total weight of the aqueous suspension of metal nanoparticle seeds.

[0106] Step (i) more particularly consists in obtaining an aqueous suspension of metal nanoparticle seeds, also called "nuclei", having a size of less than 10 nanometers.

[0107] The aqueous suspension of metal nanoparticle seeds obtained in step (i) may be allowed to age, for example for 2 hours, before being used in step (ii).

[0108] Step (ii) comprises subjecting an aqueous suspension of metal nanoparticle seeds to Dispersants such as homopolymers or copolymers of vinylpyrrolidone and / or homopolymers or copolymers of vinyl alcohol, more particularly polyvinylpyrrolidone. at least one reducing agent, more particularly two reducing agents, in particular those mentioned above, in particular a mixture of alkali metal or alkaline earth metal salts of citric acid, in particular an alkali salt of citrate, more particularly sodium citrate, such as trisodium citrate, and a further reducing agent, more particularly ascorbic acid, even more particularly a mixture of sodium citrate and ascorbic acid, and - a metal salt from the same metal as that used in step i).

[0109] In one embodiment, the gold salt is HAuCl4, optionally in the form of a trihydrate.

[0110] In one embodiment, the silver salt is at least one of AgNO3, AgClO4, Ag2SO4, AgCl, AgBr, AgOH, Ag2O, AgBF4, AgIO3, and AgPF6, and more particularly, the silver salt is an aqueous solution of AgNO3, in particular AgNO3. In particular, the silver salt is in the form of an aqueous solution of silver nitrate.

[0111] In one embodiment, the aluminum salt is at least one of AlCl3, Al(NO3)3, Al2(SO4)3, and more specifically, the aluminum salt is AlCl3.

[0112] In one embodiment, the copper salt is at least one of Cu(SO), CuCl, Cu(NO), Cu(CO, and more specifically, the copper salt is CuCl.

[0113] In one embodiment, the total amount of metal salts (silver, gold, aluminum, and / or copper salts, specifically silver and / or gold salts, more specifically silver salts) added to the aqueous suspension is in the range of 0.0005 to 0.05 wt %, specifically 0.001 to 0.01 wt %, based on the total weight of the aqueous suspension.

[0114] In another embodiment, the total amount of an alkali metal or alkaline earth metal salt of citric acid, specifically an alkali citrate, more specifically a sodium citrate such as trisodium citrate, added to the aqueous suspension is in the range of 0.001-0.1 wt %, specifically 0.005-0.05 wt %, based on the total weight of the aqueous suspension.

[0115] In certain embodiments, the total amount of ascorbic acid added in the aqueous suspension ranges from 0.0001 to 0.1% by weight, specifically, from 0.0005 to 0.05% by weight, based on the total weight of the aqueous suspension.

[0116] In a specific embodiment, the total amount of polyvinylpyrrolidone added to the aqueous suspension is in the range of 0.01 to 2% by weight, specifically 0.05 to 1% by weight, based on the total weight of the aqueous suspension.

[0117] The obtained aqueous suspension of metal nanoparticles has a fixed color.

[0118] In certain embodiments, the total amount of metal nanoparticles in the aqueous suspension ranges from 0.0001 to 0.02 wt %, specifically, from 0.0005 to 0.01 wt %, based on the total weight of the aqueous suspension.

[0119] The color may vary depending on the type of metal nanoparticles (gold, silver, aluminum, or copper) and their amount, and the amount of reducing agent used. The color may depend in particular on the proportion of an alkali metal or alkaline earth metal salt of citric acid, specifically an alkali citrate, more specifically sodium citrate such as trisodium citrate, and / or the amount of metal salt. For example, the color of the aqueous ink suspension may change from yellow to red to blue with a higher amount of an alkali metal or alkaline earth metal salt of citric acid, specifically an alkali citrate, more specifically sodium citrate such as trisodium citrate, and / or with a higher amount of silver salt if the metal salt is silver.

[0120] The process of the present invention can be carried out over a wide range of temperatures. Generally, the process is carried out within a temperature range of 0-100°C, specifically 5-70°C, more specifically 10-40°C. The relatively low process temperature contributes to process efficiency and process economy, and also meets current ecological requirements. In fact, the process of the present invention is carried out in an aqueous medium and is therefore a "green process". In addition, at low temperatures, it is advantageous that a more stable dispersion is obtained and the silver nanoparticles exhibit a smaller size. Without being bound by theory, the use of a dispersing agent such as polyvinylpyrrolidone and / or polyvinyl alcohol may help to prevent the metal nanoparticles from coming into direct contact and / or agglomerating and / or settling in the suspension.

[0121] More specifically, the preparation method comprises a concentration step (iii), which is carried out by centrifugation and / or evaporation under vacuum and / or tangential flow nanofiltration of the aqueous suspension containing the metal nanoparticles obtained in step (ii) in order to concentrate the metal nanoparticles in a suspension. A concentrated aqueous suspension of metal nanoparticles is thus obtained.

[0122] In certain embodiments, the aqueous suspension containing the metal nanoparticles can be centrifuged, for example, at 10,000 rpm for 30 minutes.

[0123] In a particular embodiment, the total amount of metal nanoparticles in the concentrated aqueous suspension is in the range of 0.01 to 10 wt %, specifically 0.05 to 5 wt %, based on the total weight of the concentrated aqueous suspension.

[0124] The aqueous writing ink (a) can then be prepared by incorporating or redispersing the concentrated suspension obtained in step (iii) or the aqueous suspension obtained in step (ii) in an aqueous writing ink composition which may also contain classical aqueous writing ink ingredients, in particular classical aqueous gel ink ingredients such as co-solvents, antimicrobial agents, corrosion inhibitors, antifoam agents, rheology modifiers, as described above.

[0125] In certain embodiments, the total amount of metal nanoparticles in the aqueous writing ink composition ranges from 0.01 to 10 wt %, specifically 0.1 to 5 wt %, based on the total weight of the aqueous writing ink composition.

[0126] The kit according to the invention also contains an eliminator fluid (b), more particularly an aqueous eliminator fluid, which contains at least one oxidizing agent.

[0127] In particular, the oxidizing agent of the eliminator fluid (b) is decomposable upon contact with light and / or air, more particularly oxygen such as oxygen O2 and ozone O3, hydrogen peroxide H2O2 and compounds capable of generating hydrogen peroxide by hydrolysis such as nitric acid, organic peroxides such as organic peroxides of methyl ethyl acetone, alkali metal bromates and persalts such as perborates and persulfates, halogens such as fluorine F2 and chlorine Cl2, permagnates, particularly permagnate salts, more particularly oxides such as potassium permanganate KMnO4, and mixtures thereof, more particularly it is hydrogen peroxide H2O2 and / or bicarbonate solution.

[0128] More specifically, oxidizing agents suitable for use in the eradicator fluid (b) according to the present invention have a redox potential higher than the redox potential of the metal of the nanoparticles of the writing ink composition (a), more specifically higher than the redox potential of gold and / or silver and / or copper and / or aluminum, even more specifically higher than the redox potential of gold and / or silver, even more specifically higher than the redox potential of silver (in particular the redox potentials of gold, silver, copper and aluminum are as follows): E(Au 3+ / Au)=1.52V E(Ag + / Ag)=0.80V E(Cu 2+ / Cu)=0.34V E(Al 3+ / Al)=-1.66V).

[0129] In certain embodiments, the total amount of oxidizing agent in the quencher fluid (b) ranges from 10 to 60% by weight, specifically, from 20 to 40% by weight, based on the total weight of the quencher fluid (b).

[0130] In certain embodiments, the quencher fluid is an aqueous fluid.

[0131] More specifically, the total amount of water in the eliminator fluid (b) is in the range of 40 to 90% by weight, specifically, 60 to 80% by weight, based on the total weight of the eliminator fluid (b).

[0132] The eradicator fluid (b) may further contain a volatile solvent, in particular one selected from ethanol, acetone, N,N-dimethylformamide (DMF), and acetonitrile, more particularly ethanol and / or N,N-dimethylformamide, and even more particularly ethanol. This solvent makes the eradicator fluid easier to dry. More specifically, the total amount of volatile solvent in the eradicator fluid (b) is in the range of 5-30% by weight, specifically 10-20% by weight, based on the total weight of the eradicator fluid (b).

[0133] The eliminator fluid (b) may also contain other additives and / or co-solvents, such as isothiazolinones (ACTICIDE® from Thor), specifically selected from the group consisting of 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and mixtures thereof.

[0134] The quencher fluid (b) can be prepared by methods well known to those skilled in the art, such as by simply mixing the oxidizer with water and optional volatile solvents and optional additives.

[0135] In certain embodiments, the aqueous writing ink composition (a) and the eradicator fluid (b) are contained in two different writing instruments. In particular, each writing instrument, - an axial barrel containing an aqueous writing ink composition (a) or an eradicator fluid (b); a pen body for delivering an aqueous writing ink composition (a) or an eradicator fluid (b) stored in the axial barrel.

[0136] The writing implement of the aqueous writing ink composition (a) may be selected from the group consisting of gel pens, felt-tip pens, and markers, and may specifically be a gel pen.

[0137] The writing implement of the erasing agent fluid (b) may be selected from the group consisting of a felt-tip pen, a correction fluid, and a marker, and may specifically be a felt-tip pen.

[0138] In another particular embodiment, the aqueous writing ink composition (a) and the eradicator fluid (b) are contained in the same writing instrument.

[0139] Specifically, the writing instrument comprises at least two separate reservoirs, more specifically, two applicator tips facing each other (particularly, at opposite ends of the writing instrument). The applicator tip for the aqueous writing ink composition (a) can be of the gel type, felt type, or marker type, specifically, of the gel type.

[0140] The applicator tip for the eraser fluid (b) can be of the gel type, felt type, correction fluid type, or marker type, specifically, the felt type.

[0141] The present invention also relates to an aqueous eradicator fluid for erasing an aqueous writing ink composition containing metal nanoparticles as colorants, more particularly as the only colorant, said metal nanoparticles consisting essentially of a metal, said metal being selected from silver, gold, aluminum and / or copper, at least one oxidizing agent, more particularly selected from the group consisting of hydrogen peroxide H2O2, oxygen, such as oxygen O2 and ozone O3, compounds capable of generating hydrogen peroxide by hydrolysis, such as nitric acid, organic peroxides, such as organic peroxides of methyl ethyl acetone, urea peroxide, alkali metal bromates and persalts, such as perborates and persulfates, halogens, such as fluorine F2 and chlorine Cl2, permagnates, more particularly permagnate salts, more particularly oxides, such as potassium permanganate KMnO4, and mixtures thereof, more particularly selected from the group consisting of hydrogen peroxide H2O2, oxygen, such as oxygen O2 and ozone O3, compounds capable of generating hydrogen peroxide by hydrolysis, such as nitric acid, organic peroxides, urea peroxides, alkali metal bromates and persalts, permagnates, more particularly permagnate salts, more particularly potassium permanganate KMnO4, and mixtures thereof, more particularly selected from the group consisting of hydrogen peroxide H2O2, oxygen, such as oxygen O2 and ozone O3, ... - an aqueous eraser fluid containing a volatile solvent such as ethanol, acetone, N,N-dimethylformamide (DMF), and acetonitrile, and mixtures thereof, more specifically, an eccentric solvent selected from ethanol and / or N,N-dimethylformamide, and even more specifically, ethanol.

[0142] In particular, the volatile solvent is a water-soluble solvent, more particularly selected from ethanol, acetone, N,N-dimethylformamide and acetonitrile, and mixtures thereof.

[0143] In certain embodiments, the total amount of volatile solvents in the aqueous eradicator fluid ranges from 5 to 30% by weight, specifically, from 10 to 20% by weight, based on the total weight of the eradicator fluid.

[0144] In certain embodiments, the total amount of oxidizer in the aqueous quencher fluid ranges from 10 to 60% by weight, specifically, from 20 to 40% by weight, based on the total weight of the quencher fluid.

[0145] In certain embodiments, the quencher fluid is an aqueous fluid.

[0146] More specifically, the total amount of water in the aqueous eliminator fluid ranges from 40 to 90% by weight, specifically, from 60 to 80% by weight, based on the total weight of the eliminator fluid.

[0147] In certain embodiments, the aqueous eradicator fluid does not contain a colorant.

[0148] In particular, the quencher fluid is as described above for the kit and can be prepared as described above.

[0149] The present invention further provides a writing instrument containing an eradicator fluid according to the present invention, comprising: an axial barrel containing an eliminator fluid according to the invention; a pen body for delivering an eradicant fluid according to the invention stored in an axial barrel, More specifically, the writing instrument is selected from the group consisting of a felt-tip pen, a correction fluid, and a marker, and even more specifically, the writing instrument is a felt-tip pen.

[0150] The present invention also relates to the use of an eliminator fluid containing at least one oxidizing agent according to the invention or contained in a kit according to the invention, - for erasing an aqueous writing ink composition containing metallic nanoparticles as the only colorant, said metallic nanoparticles consisting essentially of a metal, said metal being selected from silver, gold, aluminium and / or copper, more particularly said aqueous writing ink composition being as described above or as contained in a kit according to the invention, or - for changing the colour of an aqueous writing ink composition containing metal nanoparticles together with a further colourant, said metal nanoparticles consisting essentially of a metal, said metal being selected from silver, gold, aluminium and / or copper, said aqueous writing ink composition being in particular as described above or as contained in a kit according to the invention.

[0151] The invention further relates to a method for correcting errors in writing marks on a porous substrate by means of an aqueous writing ink composition containing metallic nanoparticles as the only colorant, the metallic nanoparticles consisting essentially of a metal, the metal being selected from silver, gold, aluminium and / or copper, the aqueous writing ink composition being in particular as described above or contained in a kit according to the invention, the method comprising the steps of: A) applying an eraser fluid according to the present invention or contained in a kit according to the present invention onto the writing mark as needed for correction until the writing mark is no longer visible to the naked eye; B) once the porous substrate has dried, in particular after at least 1 minute, an aqueous writing ink composition containing metal nanoparticles as colorant, said metal nanoparticles essentially consisting of a metal, said metal being selected from silver, gold, aluminium and / or copper, said aqueous writing ink composition being in particular contained in a kit according to the invention or overwriting the erased spots on the porous substrate with said aqueous writing ink composition as described above.

[0152] The present invention finally relates to a method for using the kit according to the invention, comprising the steps of: A1) writing on a porous substrate with an aqueous writing ink composition (a); B1) optionally erasing or changing the color of a portion of the writing mark obtained in step A1) with an eraser fluid (b) until the writing mark is no longer visible to the naked eye or the color of the writing mark has changed to the naked eye; C1) optionally, once the porous substrate has dried, in particular after at least 1 minute, writing over the erased spots of the porous substrate with the aqueous writing ink composition (a).

[0153] The invention will be better understood with reference to the examples given in a non-limiting manner.

[0154] Example 1: Kit containing an ink composition with silver nanoparticles prepared by an ex-situ process Preparation of an aqueous suspension of silver seed nanoparticles (step (i)) In the first step (i), an aqueous suspension of silver seed nanoparticles is prepared by mixing 20.59 g of distilled water, 0.00085 g of silver nitrate (9370.1 Cark Roth), 0.0013 g of trisodium citrate (S1804-500G Sigma Aldrich).

[0155] The mixture was homogenized with a homogenizer mixer at a speed of 400 rpm for 1 minute. Then, 0.000227 g of sodium borohydride NaBH4 (71321-25G Fluka Analytical) was added dropwise. The resulting yellow solution was then stored in the dark and aged for 2 hours.

[0156] Preparation of an aqueous suspension of silver nanoparticles with a fixed color (step (ii)) In a second step (ii), an aqueous suspension of silver nanoparticles with a fixed color is prepared by mixing 528.59 g of distilled water, 1.25 g of polyvinylpyrrolidone (PVP40-100G Sigma Aldrich), 5 mL of the seed solution obtained in step (i), 0.097 g of trisodium citrate (S1804-500G Sigma Aldrich), 0.044 g of ascorbic acid (A92902-100G Sigma Aldrich).

[0157] The mixture was homogenized in a homogenizer mixer at a speed of 400 rpm for 1 minute.

[0158] Then, 0.021 g of AgNO3 was slowly added to the mixture using a homogenizer mixer at a speed of 400 rpm. The color of the solution changes from colorless to yellow, red, and finally to green.

[0159] Concentration of metal nanoparticles by centrifugation (step (iii)) One minute after the last addition of AgNO3, the aqueous suspension of silver nanoparticles was centrifuged at 10000 rpm for 30 min.

[0160] During this concentration step, the aqueous suspension of silver nanoparticles was decanted and the final volume obtained after this centrifugation was 5 mL.

[0161] This final volume after the centrifugation step contains 0.014 g of Ag nanoparticles.

[0162] Furthermore, the shape of the Ag nanoparticles is mainly polyhedral and the average particle size, measured by analysis of 2D images (microscope: JEOL ARM 200), according to the ISO 9001:2015 standard, comprises 50-70 nanometers.

[0163] Preparation of water-based gel ink with fixed color An aqueous gel ink was prepared by mixing 0.53 g glycerin (co-solvent), 0.42 g polyethylene glycol (co-solvent), 0.01 g Acticide® MBS (antimicrobial agent), and 0.02 g Additin® RC8221 (corrosion inhibitor). The mixture was mixed in a homogenizer mixer at 15 m.s. -1 The mixture was homogenized for 15 minutes at a speed of 1500 rpm and heated at a temperature of 35° C. Then, 0.02 g of xanthan gum (rheology modifier) ​​was added to the mixture. The mixture was homogenized in a homogenizing mixer at a speed of 1500 rpm and heated at a temperature of 35° C. -1 The mixture was homogenized at a speed of 15 m.s for 15 minutes at a temperature of 35°C. 4.27 g of the green aqueous suspension of nanoparticles obtained in step (iii) above was slowly added to the mixture. The mixture was left to stand for 2 hours and 30 minutes. Then 0.015 g of Moussex® S 9092 (antifoaming agent) was added. The mixture was homogenized in a homogenizing mixer at a speed of 15 m.s. -1 The mixture was homogenized at a speed of 35° C. for 30 minutes at a temperature of 35° C.

[0164] The resulting aqueous gel ink was cooled at room temperature (25° C.).

[0165] The water-based gel ink is green in color. The total amount of the water-based gel ink is 5.28 g, and the water-based gel ink contains 0.22 wt % Ag nanoparticles.

[0166] Furthermore, the shape of the Ag nanoparticles is mainly polyhedral and the average particle size, measured by analysis of 2D images (microscope: JEOL ARM 200), according to the ISO 9001:2015 standard, comprises 50-70 nanometers.

[0167] Preparation of eliminator fluid (b) Three different quencher fluids are envisioned. An aqueous solution of hydrogen peroxide at -30% (w / w) was prepared as eliminator fluid (b1). A 1M sodium bicarbonate solution was prepared as the quencher fluid (b2). A mixture of 80% aqueous hydrogen peroxide at 30% (w / w) and 20% ethanol was prepared as quencher fluid (b3).

[0168] Ink erasing process The obtained aqueous ink composition (a) was applied to a porous substrate (Calligraphe LIGNE 7000, 70 g m -2 When written on a notebook (210 x 297 mm, 80 pages, Clairefontaine), the color did not change and remained green. Immediately after writing, the writing mark was erased using an eraser fluid (b1 or b2 or b3), and the color of the writing mark was erased.

[0169] After erasure (approximately 10 minutes after using the erasing agent fluid b1 or b2, and approximately 1 minute after using the erasing agent fluid b3), it was possible to overwrite the image using the same aqueous ink composition (a).

Claims

1. a) an aqueous writing ink composition, more specifically an aqueous gel ink; metal nanoparticles as colorants, more particularly as the only colorants, said metal nanoparticles consisting essentially of a metal, said metal being chosen from silver, gold, aluminium and / or copper, more particularly said metal being silver, and - an aqueous writing ink composition containing a dispersant such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and mixtures thereof; b) an quencher fluid containing at least one oxidizer.

2. 2. The kit of claim 1, wherein the ink composition (a) and the eraser fluid (b) are contained in two different writing instruments, more specifically, the writing instrument for the ink composition (a) is a gel pen, or the ink composition (a) and the eraser fluid (b) are contained in the same writing instrument, more specifically, the writing instrument contains at least two separate reservoirs, and even more specifically, the applicator tip for the aqueous writing ink composition (a) is of the gel type.

3. 3. The kit of claim 1 or 2, wherein the metal of the metal nanoparticles comprises at least silver, gold, and mixtures thereof, and more specifically, the metal nanoparticles are silver nanoparticles.

4. The kit according to any one of claims 1 to 3, wherein the aqueous writing ink composition (a) exhibits a plasmonic effect.

5. the total amount of metal nanoparticles of the aqueous writing ink composition (a) is in the range of 0.01 to 10 wt.-%, more specifically 0.1 to 5 wt.-%, based on the total weight of the aqueous writing ink composition (a); and / or the metal nanoparticles of the aqueous writing ink composition (a) have an average particle size in the range of 1 to 200 nm, specifically 2 to 100 nm, more specifically 5 to 100 nm; and / or 5. The kit according to claim 1, wherein the dispersant is selected from homopolymers or copolymers of vinylpyrrolidone and / or homopolymers or copolymers of vinyl alcohol and mixtures thereof, more particularly a homopolymer or copolymer of vinylpyrrolidone, and / or the amount of dispersant is in the range of 0.01 to 10% by weight, more particularly in the range of 0.01 to 5% by weight, based on the total weight of the aqueous writing ink.

6. The aqueous writing ink composition (a) reducing agents, more specifically alkali metal salts or alkaline earth metal salts and / or hydroxylamines (NH ２ OH), and / or ascorbic acid, and / or oxalic acid, and / or formic acid, and / or formaldehyde, and / or hydrazine, and / or substituted hydrazines, such as 1,1-dimethylhydrazine or 1,2-dimethylhydrazine, and / or sodium hydrosulfite, and / or tributylstannane, and / or tributyltin hydride, and / or triphenylphosphine, and / or triphenylphosphite, and / or trichlorosilane, and / or triethylsilane, tris(trimethylsilyl)silane, and / or polymethylhydroxysilane, and / or a reducing agent selected from the esters of retinol of formula (I). 【Chemistry 1】 wherein R is an optionally substituted C １ -C ６ Aliphatic groups, more specifically, (C １ -C ６ ) alkyl groups, and / or citric acid and / or derivatives of citric acid selected from esters, amides and thioesters of citric acid, salts of citric acid or said derivatives, solvates of citric acid or said derivatives such as hydrates, and mixtures thereof, and / or N-acyl-aminophenols, the hydroxyl group being preferably in the meta or para position of the benzene group, preferably in the para position, preferably N-acyl-aminophenols of formula HO-R1-NH-CO-R2, in which R1 is a benzene ring and R2 is an alkyl group preferably containing 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, preferably the hydroxyl group being in the meta or para position, preferably in the para position, and / or - alkali metal hydrides, in particular sodium borohydride NaBH ４ The kit according to any one of claims 1 to 5, further comprising an alkali metal hydride,

7. The kit according to any one of claims 1 to 6, wherein the aqueous writing ink composition (a) further comprises a co-solvent, an antimicrobial agent, a corrosion inhibitor, an antifoaming agent, and / or a rheology modifier.

8. The oxidizing agent of the eliminator fluid (b) is oxygen O ２ and ozone O ３ Oxygen, hydrogen peroxide, etc. ２ O ２ and nitric acid, organic peroxides such as the organic peroxide of methyl ethyl acetone, alkali metal bromates and persalts such as urea peroxide, perborates and persulfates, fluorine F ２ and chlorine Cl ２ Halogens such as permagnates, more specifically permagnate salts, more specifically potassium permanganate KMnO ４ and / or mixtures thereof. The kit of any one of claims 1 to 7, wherein the eliminator fluid (b) further comprises a volatile solvent, such as ethanol, acetone, N,N-dimethylformamide, and acetonitrile, and mixtures thereof.

9. A method for correcting errors in writing marks on a porous substrate by means of an aqueous writing ink composition containing metallic nanoparticles as the only colorant, said metallic nanoparticles consisting essentially of a metal, said metal being selected from silver, gold, aluminium and / or copper, said aqueous writing ink composition being as specifically described in any one of claims 1 and 3 to 7 or being contained in a kit according to any one of claims 1 to 8, said method comprising: A) applying the eraser fluid contained in the kit according to any one of claims 1 to 8 onto the written mark as needed for correction until the written mark is no longer visible to the naked eye; B) once the porous substrate has dried, writing over the erased spots on the porous substrate with an aqueous writing ink composition containing metal nanoparticles as the colorant, said metal nanoparticles consisting essentially of a metal, said metal being selected from silver, gold, aluminium and / or copper, said aqueous writing ink composition being specifically contained in a kit according to any one of claims 1 to 8 or according to any one of claims 1 and 3 to 7.

10. A method of using the kit according to any one of claims 1 to 8, comprising the steps of: A1) writing on a porous substrate with the aqueous writing ink composition (a); B1) optionally erasing or changing the color of a portion of the writing mark obtained in step A1) with the eraser fluid (b) until the writing mark is no longer visible to the naked eye or the color of the writing mark has changed to the naked eye; C1) optionally, once said porous substrate has dried, writing over said erased spots of said porous substrate with said aqueous writing ink composition (a).

11. An aqueous writing ink composition, more specifically an aqueous gel ink, - metallic nanoparticles as colorants, more particularly as the only colorants, said metallic nanoparticles consisting essentially of a metal, said metal being chosen from silver, gold, aluminium and / or copper, more particularly said metal being silver; - a dispersing agent such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and mixtures thereof; - a reducing agent comprising ascorbic acid.

12. 12. The water-based writing ink of claim 11, wherein said metal nanoparticles are the only colorant.

13. 13. A water-based writing ink according to claim 11 or 12, wherein the metal of the metal nanoparticles comprises at least silver, gold and mixtures thereof, more particularly at least silver nanoparticles.

14. The reducing agent is - alkali metal salts or alkaline earth metal salts and / or hydroxylamines (NH ２ OH), and / or oxalic acid, and / or formic acid, and / or formaldehyde, and / or hydrazine, and / or substituted hydrazines, such as 1,1-dimethylhydrazine or 1,2-dimethylhydrazine, and / or sodium hydrosulfite, and / or tributylstannane, and / or tributyltin hydride, and / or triphenyl-phosphine, and / or triphenylphosphite, and / or trichlorosilane, and / or triethylsilane, tris(trimethylsilyl)silane, and / or polymethylhydroxysilane, and / or esters of retinol of formula (I) 【Chemistry 2】 wherein R is an optionally substituted C １ -C ６ Aliphatic groups, more specifically, (C １ -C ６ ) alkyl groups, and / or citric acid and / or derivatives of citric acid selected from esters, amides and thioesters of citric acid, salts of citric acid or said derivatives, solvates of citric acid or said derivatives such as hydrates, and mixtures thereof, and / or N-acyl-aminophenols, the hydroxyl group being preferably in the meta or para position of the benzene group, preferably in the para position, preferably N-acyl-aminophenols of formula HO-R1-NH-CO-R2, in which R1 is a benzene ring and R2 is an alkyl group preferably containing 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, preferably the hydroxyl group being in the meta or para position, preferably in the para position, and / or - alkali metal hydrides, in particular sodium borohydride NaBH ４ 14. The water-based writing ink according to claim 11, further comprising an alkali metal hydride,

15. The reducing agent is from alkali metal and / or alkaline earth metal salts of citrates and / or chlorides and / or carbonates, more particularly from alkali citrates and / or alkali chlorides and / or alkali carbonates, even more particularly from sodium citrate and / or magnesium chloride and / or calcium chloride, even more particularly from sodium citrate and / or - alkali metal hydrides, specifically sodium borohydride NaBH ４ The water-based writing ink according to any one of claims 11 to 13, further comprising:

16. The reducing agent is sodium citrate and sodium borohydride NaBH ４ The water-based writing ink according to any one of claims 11 to 13, further comprising:

17. 1. A method for preparing an aqueous suspension containing metal nanoparticles, the method comprising: - alkali metal or alkaline earth metal salts of citric acid, in particular the alkali salts of citrate, and even more particularly sodium citrate, - Alkali metal hydrides, specifically NaBH ４ , and - a mixture of ascorbic acid, The process is prepared by mixing in the presence of a dispersing agent as described above, such as a homopolymer or copolymer of vinylpyrrolidone and / or a homopolymer or copolymer of vinyl alcohol, and more particularly polyvinylpyrrolidone.

18. 20. The method of claim 17, wherein the metal of the metal nanoparticles comprises at least silver, gold, and mixtures thereof, and more specifically comprises at least silver nanoparticles.

19. - step (i) of preparing an aqueous suspension of said seeds of said metal nanoparticles, comprising dissolving metal salts such as silver, gold, aluminium and / or copper salts, in particular silver and / or gold salts, more particularly silver salts, in water and an alkali metal or alkaline earth metal salt of citric acid, in particular an alkali citrate, more particularly sodium citrate, such as trisodium citrate, and an alkali metal hydride, in particular NaBH ４ , and more specifically, sodium citrate and NaBH ４ With a mixture of - said aqueous suspension obtained in step (i), dispersants such as homopolymers or copolymers of vinylpyrrolidone and / or homopolymers or copolymers of vinyl alcohol, more particularly polyvinylpyrrolidone; - alkali metal or alkaline earth metal salts of citric acid, specifically alkali citrates, more specifically mixtures of sodium citrate, such as trisodium citrate, with ascorbic acid, and even more specifically mixtures of sodium citrate and ascorbic acid, and - step (ii) carried out by mixing with a metal salt from the same metal as that used in step i); - optionally a step (iii) of concentrating the metal nanoparticles, in particular by centrifugation of the aqueous suspension obtained in step (ii) and / or evaporation under vacuum and / or tangential flow nanofiltration.

20. 20. A method for preparing an aqueous writing ink by incorporating or redispersing an aqueous suspension comprising the metal nanoparticles according to any one of claims 17 to 19 in an aqueous writing ink composition comprising one or more ingredients selected from co-solvents, antimicrobial agents, corrosion inhibitors, antifoam agents, and rheology modifiers.

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