CA3197947A1

CA3197947A1 - Compositions, comprising silver nanoplatelets

Info

Publication number: CA3197947A1
Application number: CA3197947A
Authority: CA
Inventors: Nikolay A. Grigorenko; Andre OSWALD
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2020-11-10
Filing date: 2021-11-09
Publication date: 2022-05-19
Also published as: EP4244003A1; WO2022101207A1; CN116547090A; AU2021379955A1

Abstract

The present invention relates to compositions, comprising silver nanoplatelets capped by dithiocarbamate anions of formula (XX), Formula (XX). UV-Vis radiation curable inks, containing the silver nanoplatelets, do not degrade and a coating, comprising the composition, shows a blue color in transmission and a metallic yellow color in reflection.

Description

Compositions, comprising silver nanoplatelets The present invention relates to compositions, comprising silver nanoplatelets capped by dithiocarbamate anions of formula (XX). UV-Vis radiation curable inks, containing the silver nanoplatelets, do not degrade and a coating, comprising the composition, shows a blue color in transmission and a metallic yellow color in reflection.
US2017246690 (EP3157697) discloses a method for synthesizing metal nanoparticles, the method comprising:
(a) preparing a metal precursor mixture comprising a metal precursor compound and a first aqueous liquid medium, (b) preparing a reducing agent mixture comprising a reducing agent and a second aqueous liquid medium, (c) optionally adding an acid or a base to the mixture prepared in step (a) or to the mixture prepared in step (b), wherein the metal precursor mixture and the reducing agent mixture are both free of stabilizing agent and free of seed particles, (d) combining the metal precursor mixture with the reducing agent mixture so as to allow the metal precursor compound to react with the reducing agent, thereby synthesizing the metal nanoparticles.
EP3156156 relates to a fine silver particle dispersion, which comprises fine silver particles, a short chain amine having 5 or less carbon atoms and a highly polar solvent, and a partition coefficient logP of the short chain amine is -1.0 to 1.4. The method for producing the fine silver particles of EP3156156 comprises a first step for preparing a mixed liquid of a silver compound which is decomposed by reduction to produce a metal silver, and a short chain amine having a partition coefficient logP of -1.0 to 1.4, and a second step for reducing the silver compound in the mixed liquid to produce a fine silver particle where a short chain amine having 5 or less carbon atoms which is adhered to at least a part of the surface of the particle.
EP2559786 discloses a method comprising:
a) providing a substrate;
b) applying an aqueous catalyst solution to the substrate, the aqueous catalyst solution comprises nanoparticles of one or more metal chosen from silver, gold, platinum, palladium, iridium, copper, aluminum, cobalt, nickel and iron, and one or more stabilizing compounds chosen from gallic acid, gallic acid derivatives and salts thereof, the aqueous catalyst solution is free of tin; and c) electrolessly depositing metal onto the substrate using an electroless metal plating bath.
US9028724 discloses a method for preparing a dispersion of nanoparticles, comprising:
dispersing nanoparticles having hydrophobic ligands on the surface in a hydrophobic

2 solvent to form a first dispersion; mixing the first dispersion with a surface modification solution comprising (a) at least one wetting-dispersing agent selected from polydimethylsilane, alkylol ammonium salt of an acidic polyester and alkylol ammonium salt of a polyacrylic acid, (b) a surfactant, and (c) an aqueous-based solvent to form a first mixture solution; mixing the first mixture solution with a ligand removal agent to form a second mixture solution containing hydrophilic nanoparticles and separating the hydrophilic nanoparticles from the second mixture solution; and dispersing the hydrophilic nanoparticles in an aqueous-based solvent, wherein the nanoparticles comprise one of a metal and a metal oxide.
EP2667990B1 relates to a process comprising:
forming an insoluble complex of a metal salt from a reaction mixture comprising a solvent, a first surfactant, a second surfactant, and a third surfactant, each surfactant being present in the insoluble complex of the metal salt, and reacting the insoluble complex of the metal salt with a reducing agent in the reaction mixture to form metal nanoparticles;
wherein the first surfactant comprises a primary amine, the second surfactant comprises a secondary amine, and the third surfactant comprises a chelating agent comprising N,N'-dialkylethylenediamine.
EP1791702B9 relates to an ink for ink-jet printing or digital printing comprising a vehicle and metallic particles having a weight average particle size of from 40 nm to 1 micrometres, preferably from 50 nm to 500 nm, wherein the loading of metallic nanoparticles in the ink is comprised between 2 percent by weight and 75 percent by weight, preferably from 2 percent to 40 percent by weight, and the viscosity of the ink is comprised between 10 and 40 CF.
W009/056401 relates to a method for the synthesis, isolation and re-dispersion in organic matrixes of nano-shaped transition metal particles, selected from the group consisting of Zn, Ag, Cu, Au, Ta, Ni, Pd, Pt, Co, Rh, Ir, Fe, Ru, and Ti, comprising a) adding to an aqueous solution of the transition metal salt an acrylate or methacrylate monomer or oligomer, or a polyacrylate or polymethacrylate and a reducing agent;
b1) treating the colloidal solution with a peroxide; or b2) exposing the colloidal solution to UV- or visible light;
c) adding a water-soluble amine; and d) isolating the nano-shaped transition metal particles or re-disperse the nano-shaped transition metal particles together with a dispersing agent in a liquid acrylate or methacrylate monomer.
W02010108837 relates to a method of manufacturing shaped transition metal particles in the form of nanoplatelets, which metal is selected from the group consisting of Cu, Ag, Au, Zn, Cd, Ti, Cr, Mn, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt, which method comprises the steps

3 of first a) adding a reducing agent to an aqueous mixture comprising a transition metal salt and a polymeric dispersant, and subsequently b) treating the obtained colloidal dispersion with a peroxide, wherein the aqueous mixture in step a) comprises the transition metal salt in a concentration of higher than 2 mmol per liter.
W011064162 relates to security, or decorative element, comprising a substrate, which may contain indicia or other visible features in or on its surface, and on at least part of the said substrate surface, a coating comprising platelet shaped transition metal particles having a longest dimension of edge length of from 15 nm to 1000 nm, preferably from 15 nm to 600 nm and particularly from 20 nm to 500 nm, and a thickness of from 2 nm to 100 nm, preferably from 2 to 40 nm and particularly from 4 to 30 nm and a method for forming for forming an optically variable image (an optically variable device) on a substrate comprising the steps of: forming an optically variable image (OVI) on a discrete portion of the substrate;
and depositing a coating composition comprising platelet shaped transition metal particles having a longest dimension of edge length of from 15 nm to 1000 nm, preferably from 15 nm to 600 nm and particularly from 20 nm to 500 nm, and a thickness of from 2 nm to 100 nm, preferably from 2 to 40 nm and particularly from 4 to 30 nm and a binder on at least a portion of the OVI.
W02013/186167 discloses a method for forming a surface relief microstructure, especially an optically variable image (an optically variable device, OVD) on a substrate comprising the steps of:
A) applying a curable composition to at least a portion of the substrate wherein the curable composition comprises al) at least one ethylenically unsaturated resin, a monomer or a mixture thereof;
a2) at least one photoinitiator; and a3) a metal pigment which is in the form of platelet shaped transition metal particles having a longest dimension of edge length of from 5 nm to 1000 nm, preferably from 7 nm to 600 nm and particularly from 10 nm to 500 nm, and a thickness of from 1 nm to 100 nm, preferably from 2 to 40 nm and particularly from 3 to 30 nm;
B) contacting at least a portion of the curable composition with a surface relief microstructure, especially optically variable image forming means;
C) curing the composition by using at least one UV lamp.
W02014/041121 and W02014/187750 relates to a security elements, comprising a coating comprising platelet shaped transition metal particles having a longest dimension of edge length of from 15 nm to 1000 nm, preferably from 15 nm to 600 nm and particularly from 20 nm to 500 nm, and a thickness of from 2 nm to 100 nm, preferably from 2 to 40 nm and particularly from 4 to 30 nm.
W02020/083794 relates to compositions, comprising silver nanoplatelets, wherein the mean diameter of the silver nanoplatelets, present in the composition, is in the range of 20

4 to 70 nm with standard deviation being less than 50% and the mean thickness of the silver nanoplatelets, present in the composition, is in the range of 5 to 30 nm with standard deviation being less than 50%, wherein the mean aspect ratio of the silver nanoplatelets is higher than 1.5, a process for its production, printing inks containing the compositions and their use in security products. The highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition being within the range of 450 to 550 nm. A coating, comprising the composition, shows a red, or magenta color in transmission and a greenish-metallic color in reflection.
W02020/224982 relates to compositions, comprising silver nanoplatelets, wherein the number mean diameter of the silver nanoplatelets, present in the composition, is in the range of 50 to 150 nm with standard deviation being less than 60% and the number mean thickness of the silver nanoplatelets, present in the composition, is in the range of 5 to 30 nm with standard deviation being less than 50%, wherein the mean aspect ratio of the silver nanoplatelets is higher than 2.0 and the highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition being within the range of 560 to 800 nm. A coating, comprising the composition, shows a blue color in transmission and a metallic yellow color in reflection.
Dithiocarbamate capped silver, or gold nanoparticles are, for example described in Y. Liu et al., Chem. Commun. 2008, 2140-2142; A. Wei et al., J. AM. CHEM. SOC. 127 (2005) 7328-7329; P. D. Beer et al., The Royal Society of Chemistry, Dalton Trans., 2007, 1459-1472, V. M. Rotello et al., Adv. Mater. 2008, 20, 4185-4188 and Y. Huang et al., Analyst, 2013, 138, 2420-2426.
It has now been found, surprisingly, that silver nanoplatelets capped by dithiocarbamate anions of formula (XX) have excellent stability of optical properties upon storage or heat exposure and high colloidal stability. Silver nanoplatelets surface-modified in this way can be formulated in screen, rotogravure and flexography printing inks, which upon printing exhibit blue color in transmission and metallic yellow color in reflection and show excellent shelf stability.
Accordingly, the present application relates to compositions, comprising silver nanoplatelets, wherein the silver nanoplatelets are capped by dithiocarbamate anions of S-formula (XX), wherein R" is a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R42 is a Ci-C4alkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups.
The number mean diameter of the silver nanoplatelets, present in the composition, is

5 preferably in the range of 50 to 150 nm. The standard deviation being preferably less than 60%. The number mean thickness of the silver nanoplatelets, present in the composition, is preferably in the range of 5 to 30 nm. The standard deviation being preferably less than 50%.
The number mean diameter and the number mean thickness are determined by transmission electron microscopy (TEM).
The mean aspect ratio of the silver nanoplatelets is preferably higher than 2Ø The highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition being within the range of 560 to 800 nm.
In principle, any type of silver nanoparticles can be capped by dithiocarbamate anions of formula (XX). It is preferred that the silver nanoparticles are anisotropic (non-spherical).
Most preferred are silver nanoplatelets. The silver nanoplatelets may be in the form of disks, regular hexagons, triangles, especially equilateral triangles, and truncated triangles, especially truncated equilateral triangles, or mixtures thereof. They are preferably in the form of disks, truncated triangles, hexagons, or mixtures thereof.
The term "silver nanoplatelets" is a term used in the art and as such is understood by the skilled person. In the context of the present invention, silver nanoplatelets are preferably any silver nanoplatelets having a number mean diameter in the range of 50 to 150 nm and a number mean thickness in the range of 5 to 30 nm. The mean aspect ratio being higher than 2Ø
In the context of the present invention, a "surface modified silver nanoplatelet (nanoparticle)" is a silver nanoplatelet (nanoparticle) having attached to its surface one or more (surface) stabilizing agents.
Accordingly, the present invention relates to surface modified silver nanoplatelets capped by dithiocarbamate anions of formula (XX) and optionally bearing further surface stabilizing agent(s) and further stabilizing agents described below on their surface.
The number mean diameter of the silver nanoplatelets is in the range of 50 to 150 nm, preferably 60 to 140 nm, more preferably 70 to 120 nm. The standard deviation being preferably less than 60%, more preferred less than 50%.

6 The diameter of a silver nanoplatelet is the longest dimension of said silver nanoplatelet and corresponds to the maximum dimension of said silver nanoplatelet when oriented parallel to the plane of a transmission electron microscopy (TEM) image. As used herein, the term "number mean diameter of the silver nanoplatelets" refers to the mean diameter determined by transmission electron microscopy (TEM) using Fiji image analysis software (or Image analysis software: ParticleSizer (Thorsten Wagner (2016) ij-particlesizer:
ParticleSizer 1Ø9.
Zenodo; 10.5281/zenodo.820296) and ImageJ version 1.53f51) based on the measurement of at least 300, especially at least 500 randomly selected silver nanoplatelets oriented parallel to the plane of a transmission electron microscopy image (TEM), wherein the diameter of a silver nanoplatelet is the maximum dimension (maximum Feret diameter) of said silver nanoplatelet oriented parallel to the plane of a transmission electron microscopy (TEM) image. TEM analysis was conducted on a dispersion containing silver nanoplatelets in isopropanol using an EM 910 instrument from ZEISS (INST.109) in bright field mode at an e-beam acceleration voltage of 100kV.
The number mean thickness of the silver nanoplatelets is in the range of 5 to 30 nm, preferably 7 to 25 nm, more preferably 8 to 25 nm. The standard deviation being preferably less than 50%, more preferred less than 30%.
The thickness of a silver nanoplatelet is the shortest dimension of said nanoplatelet and corresponds to the maximum thickness of said silver nanoplatelet. As used herein, the term "number mean thickness of silver nanoplatelets" refers to the mean thickness determined by transmission electron microscopy (TEM) based on the measurement of at least 50, especially of at least 300 randomly selected silver nanoplatelets oriented perpendicular to the plane of the TEM image, wherein the thickness of the silver nanoplatelet is the maximum thickness of said silver nanoplatelet. TEM analysis was conducted on a dispersion containing silver nanoplatelets in isopropanol using an EM 910 instrument from ZEISS (INST.109) in bright field mode at an e-beam acceleration voltage of 100kV.
The thickness of at least 300 randomly selected silver nanoplatelets may be determined from the cross-sectional TEM images by fitting ellipses to the cross-sectioned particles by the software (ParticleSizer). The minor axis (the shortest diameter) of the fitted ellipse is taken as particle thickness.
The diameter is the longer side of the nanoplatelet (width). The thickness is the shorter side of the nanoplatelet (height).
The mean aspect ratio (defined as the ratio of number mean diameter to number mean thickness) being larger than 2.0, preferably larger than 2.2 and more preferably larger than 2.5.

7 The aspect ratio of the nanoplatelets is the ratio of its longest dimension, such as, for example, its diameter to its shortest dimension, such as, for example, its thickness. For example, the aspect ratio of a disk is the ratio of its diameter to its thickness.
In a particularly preferred embodiment the number mean diameter of the silver nanoplatelets is in the range of 70 to 120 nm with standard deviation being preferably less than 50% and the number mean thickness of the silver nanoplatelets is in the range of 8 to 25 nm with standard deviation being preferably less than 30%. The mean aspect ratio of the silver nanoplatelets is higher than 2.5.
The highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition being within the range of 560 to 800 nm, preferably 580 to 800 nm, most preferably 600 to 800 nm (measured in water at ca. 5*10-5 M (mo1/1) concentration of silver).
The absorption maximum has a full width at half maximum (FWHM) value in the range of 50 to 500 nm, preferably 70 to 450 nm, more preferably 80 to 450 nm.
The molar extinction coefficient of silver nanoplatelets, measured at the highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition, is higher than 4000 L/(cm*molAg), especially higher than 5000 L/(cm*molAg), very especially higher than 6000 U(cm"molAq).
The silver nanoplatelets are capped by dithiocarbamate anions of formula S -R
(XX), wherein R41 is a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R42 is a C1-C4alkyl group, or a 02-C4alkyl group, which is substituted by one, or two hydroxy groups.
In a preferred embodiment R42 is a Cl-atalkyl group and R41 is a 02-C4alkyl group, which is substituted by two hydroxy groups. In a more preferred embodiment R41 is a C2-C4alkyl group, which is substituted by one hydroxy group and R42 is a C2-C4alkyl group, which is substituted by one hydroxy group. In said embodiment R41 and R42 are independently of each other selected from the group consisting of: -CH2CH2OH, -CH2CH(OH)CH3, -CH2CH2CH2OH, -CI(CH3)(CH2OH),-CH2CH(OH)CH2CH3, -CH2CH2CH(OH)CH3 -CH2CH2CH2CH2OH, -CH(CH3)CH(OH)CH3, -CH(CH2OH)CH2CH3, -CH(CH3)CH2CH2OH, -CH2CH(CH2OH)CH3, -CH2C(CH3)(OH)CH3, -CH2CH(CH3)CH2(OH), -CH2C(OH)(CH3)2, -

8 CH2C(CH3)(CH2OH), more preferably selected from the group consisting of:
¨CH2CH2OH, ¨
CH2CH(OH)CH3, and ¨CH2CH2CH2OH.
C1-C4alkyl may be linear and branched and is typically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, or tert.-butyl.
02-C4alkyl group, which is substituted by one, or two hydroxy groups, may be linear and branched and is typically ethyl, n-propyl, isopropyl, n-butyl, sec.-butyl, isobutyl, or tert.-butyl, wherein one, or two hydrogen atoms are replaced by hydroxy groups. Examples are a -CH2CH(OH)CH2OH group, a ¨CH(CH2OH)2 group, a -CH2CH2OH group, a -CH2CH(OH)CH3 group and a -CH2CH2CH2OH group.
R41 and R42 may be different, but are preferably the same and represent especially a -CH2CH2OH group, a -CH2CH(OH)CH3 group, or a -CH2CH20H201--I group; very especially a -CH2CH2OH group.
Examples of preferred dithiocarbamate anions of formula (XX) are HO HO
\-----\ s- )-----A s-/------/N-----< >/N
HO S HO S
(E-1), (E-2) and HO
----\-------\ S-N-___<
HO S
(E-3). The dithiocarbamate anion (E-1) is most preferred.
The dithiocarbamate capped silver nanoplatelets may be prepared i) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets; or ii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and a base; or

9 iv) by reacting CS2 with an amine of formula R41R42NH in the presence of a base to obtain a ¨ _ N s- Catk+
S
compound of formula ¨ - k (XXI), which is then reacted with a composition of silver nanoplatelets; wherein R41 and R42 are defined above, or below, Cat" is a cation and k is 1, or 2.
In case of ii) and iii) the base is preferably selected from alkali or alkaline earth metal hydroxides, alkali or alkaline earth metal alkoxides, amines and quaternary ammonium hydroxides and mixtures thereof.
In case of iv) the base is preferably selected from alkali or alkaline earth metal hydroxides, alkali or alkaline earth metal alkoxides and mixtures thereof.
In case of iii) and iv) the obtained dispersions may comprise small amounts of xanthate salts.
More preferably, the base is selected from alkali metal hydroxides, such as, for example, NaOH, KOH and Cs0H, alkali metal alkoxides, such as, for example, NaOCH2CH3, KOCH2CH3 and CsOCH2CH3, amines of formula R431-i'-'44R45N, especially (HOCH2CH2)2NH
and (HOCH2CH2)3N, and mixtures thereof.
With respect to the compound of formula (XXI) the same preferences apply for R41 and R42 as in case of formula (XX) and Cat' is selected from H+, alkali metal cations, alkaline earth metal cations and R43R44 R45Nn"4, such as, for example, (HOCH2CH2)2NH2+ and (HOCH2CH2)3NH+, and mixtures thereof and is preferably selected from alkali metal cations, (HOCH2CH2)2NH2+, (HOCH2CH2)3NH+ and mixtures thereof. Cat k+ is more preferably selected from alkali metal cations and (HOCH2CH2)2NH2+ and mixtures thereof, most preferred from Cs, K+, RV, Na + and (HOCH2CH2)2NH2+ and mixtures thereof.
R43 is a 02-C4alkyl group, which is substituted by one, or two hydroxy groups, R44 is a Ci-C4alkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R45 is H, a C1-C4alkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups. Preferably, R43 is a 02-C4alkyl group, which is substituted by one hydroxy group, R44 is a 02-C4alkyl group, which is substituted by one hydroxy group, and R45 is H, or or a C2-C4alkyl group, which is substituted by one hydroxy group.

R43 and R44 may be different, but are preferably the same and represent especially a -CH2CH2OH group, a -CH2CH(OH)CH3 group, or a -CH2CH2CH2OH group; very especially a -CH2CH2OH group. R45 is preferably a hydrogen atom, a -CH2CH2OH group, a -5 CH2CH(OH)CH3 group, or a -CH2CH2CH2OH group; more preferably a hydrogen atom, or a -CH2CH2OH group and most preferred a hydrogen atom.
In a particularly preferred embodiment the dithiocarbamate capped silver nanoplatelets are prepared

10 i) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets, ii) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets and a base; wherein the base is selected from alkali metal hydroxides, alkali metal alcoholates and amines of formula R431-1R45N and mixtures thereof, wherein R43 is a C2-C4alkyl group, which is substituted by one hydroxy group, R44 is a 02-C4alkyl group, which is substituted by one hydroxy group, and R45 is H, or a 02-C4alkyl group, which is substituted by one hydroxy group, especially H;
iv) by reacting CS2 with diethanolamine in the presence of alkali metal alcoholates, or alkali HO
S- Car metal hydroxides to obtain a compound of formula (XXIa), wherein Cat+ is an alkali metal cation and then reacting the compound of formula (XXIa) with a composition of silver nanoplatelets.
The cation of the dithiocarbamate anion varies dependent on the preparation process of the dithiocarbamate capped silver nanoplatelets.
Accordingly, the present invention relates to compositions, comprising silver nanoplatelets, wherein the silver nanoplatelets are capped by a compound of formula S Catk+
R4%'--Ny _ k (XXI), wherein

11 R41 is a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R42 is a Ci-C4alkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups;
Cat k+ is a cation and k is 1, or 2.
In a preferred embodiment R42 is a 01-C4alkyl group and R41 is a 02-C4alkyl group, which is substituted by two hydroxy groups. In a more preferred embodiment 1:141 is a C2-C4alkyl group, which is substituted by one hydroxy group and R42 is a 02-C4alkyl group, which is substituted by one hydroxy group.
R41 and R42 may be different, but are preferably the same and represent especially a -CH2CH2OH group, a -CH2CH(OH)CH3 group, or a -CH2CH2CH2OH group; very especially a -CH2CH2OH group.
Cat k+ is selected from 1-1 , alkali metal cations, alkaline earth metal cations and R43R44R45N¨ri , such as, for example, (HOCH2CH2)2NH2+ and (HOCH2CH2)3NH+, and mixtures thereof and is preferably selected from alkali metal cations, (HOCH2CH2)2NH2+, (HOCH2CH2)3NH+ and mixtures thereof. Cat k+ is more preferably selected from alkali metal cations and (HOCH2CH2)2NH2+ and mixtures thereof, most preferred from Cs, K+, Rb+, Na+
and (HOCH2CH2)2NH2+ and mixtures thereof.
Examples of dithiocarbamate salts of general formula (XXI) include, but are not limited to, sodium bis(2-hydroxyethyl)dithiocarbamate, potassium bis(2-hydroxyethyl)dithiocarbamate, cesium bis(2-hydroxyethyl)dithiocarbamate, sodium bis(3-hydroxypropyl)dithiocarbamate, bis(3-hydroxypropyl)dithiocarbamate, cesium bis(3-hydroxypropyl)dithiocarbamate, sodium bis(4-hydroxybutyl)dithiocarbamate, bis(4-hydroxybutyl)dithiocarbamate, and cesium bis(4-hydroxybutyl)dithiocarbamate.
The surface stabilizing agent of general formula (XXI) may be present in an amount from about 0.4% to about 5%, preferably from about 0.5% to about 3.5% of the weight percent (wt-%) of the silver nanoplatelets.
Examples of compounds of formula (XXI) are listed below:
HO
S K+

(21 a), which may be obtained by reacting CS2 with diethanolamine in the presence of potassium 01-C8alcoholate, especially potassium ethanolate, or potassium hydroxide;

12 HO
\------N SCs /............../N.¨.__<

(21b), which may be obtained by reacting CS2 with diethanolamine in the presence of cesium C1-C8alcoholate, especially cesium ethanolate, or cesium hydroxide;
HO
\----A SNa /....___\<
HO S
(21c), which may be obtained by reacting CS2 with diethanolamine in the presence of sodium Ci-Csalcoholate, especially sodium ethanolate, or sodium hydroxide; and HO
\--------\ _4-S NH2((CH2)20H)2 /..,.......... _./.........<

(21d), which is obtained by reacting CS2 with diethanolamine. Compounds (21a), (21b) and (21c) are more stable and are preferred.
In reaction sequences iv) it is preferred that the compound of formula (XXI) is reacted with the silver nanoplatelets immediately after preparation.
The in-situ synthesis of the dithiocarbamate anions in the presence of the silver nanoplatelets, i.e. reaction sequences i), ii) and iii) are more preferred.
In addition to the capping agent(s) of formula (XX) the composition may comprise one, or more surface stabilizing agent(s).
In a preferred embodiment of the present invention the silver nanoplatelets bear a surface stabilizing agent of formula

13 R3 R4 R7 0 k4 (I) on their surface, wherein indicates the bond to the silver, R1 is H, Ci-Cisalkyl, phenyl, Ci-Csalkylphenyl, or CH2000H;
R2, R3, R4, R6, R6 and R7 are independently of each other H, Cl-Csalkyl, or phenyl;
Y is 0, or NR8;
R8 is H, or C1-C8alkyl;
k1 is an integer in the range of from 1 to 500, k2 and k3 are independently of each other 0, or integers in the range of from 1 to 250;
k4 is 0, or 1, k5 is an integer in the range of from 1 to 5.
Y is preferably 0. k4 is preferably 0.
The surface stabilizing agent of formula (I) has preferably a number average molecular weight of from 1000 to 20000, and more preferably from 1000 to 10000, most preferred from 1000 to 6000. All molecular weights specified in this text have the unit of [g/mol] and refer, unless indicated otherwise, to the number average molecular weight (Mn).
If the compounds comprise, for example, ethylene oxide units (E0) and propylene oxide units (PO), the order of (EO) and (PO) may be fixed (block copolymers), or may not be fixed (random copolymers).
Preferably, R1 is H, or Ci-Cisalkyl; R2, R3, R4, R6, R6 and R7 are independently of each other H, CH3, or C2H5; k1 is 22 to 450, k2 and k3 are independently of each other 0, or integers in the range of from 1 to 250; k4 is 0, or 1; and k5 is an integer in the range of from 1 to 5.
More preferred, R is H, or Ci-Caalkyl; R2, R3, R4, R6, R6 and R7 are independently of each other H, or CH3; k1 is 22 to 450; k2 and k3 are independently of each other 0, or integers in the range of from 1 to 100; k4 is 0; k5 is an integer in the range of from 1 to 4.
The most preferred surface stabilizing agent has the formula r _ Id (la), wherein R1 is H, or a Cl-Csalkyl group, and k1 is 22 to 450, especially 22 to 150.
R1 is preferably H, or CH3.

14 The preferred surface stabilizing agents are derived from MPEG thiols (poly(ethylene glycol) methyl ether thiols) having an average Mn of 2000 to 6000, such as, for example, MPEG
2000 thiol (A-1, average Mn 2,000), MPEG 3000 thiol (A-2), MPEG 4000 thiol (A3) MPEG
5000 thiol (A-4), MPEG 6000 thiol (A-5), PEG thiols (0-(2-mercaptoethyl)-poly(ethylene glycol)) having an average Mn of 2000 to 6000, such as, for example, PEG 2000 thiol (A-6, average Mn 2,000), PEG 3000 thiol (A-7), PEG 4000 thiol (A-8), PEG 5000 thiol (A-9), PEG
6000 thiol (A-10).
In another preferred embodiment of the present invention the silver nanoplatelets bear a surface stabilizing agent which is a polymer, or copolymer described in W0200674969, which can be obtained by a process comprising the steps i1) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one nitroxylether having the structural element N¨O¨X
wherein X represents a group having at least one carbon atom and is such that the free radical X. derived from X is capable of initiating polymerization; or i2) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one stable free nitroxyl radical N-0. and a free radical initiator;
wherein at least one monomer used in the steps i1) or 12) is a Cl-CÃ alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid; and optionally ii) a second step, comprising the modification of the polymer or copolymer prepared under VI) or 12) by a transesterification reaction, an amidation, hydrolysis or anhydride modification or a combination thereof.
The monomer in step i1) or 12) is preferably selected from 4-vinyl-pyridine or pyridinium-ion, 2-vinyl-pyridine or pyridinium-ion, 1-vinyl-imidazole or imidazolinium-ion, or a compound of formula CH2=C(Ra)-(C=Z)-Rb, wherein Ra is hydrogen or methyl, Rb is NH2, 0-(Me+), unsubstituted Ci-Cisalkoxy, C2-Ciooalkoxy interrupted by at least one N and/or 0 atom, or hydroxy-substituted Ci-Cisalkoxy, unsubstituted Ci-Cisalkylamino, unsubstituted, dori(C-Ni-Cisalkyl)amino, hydroxy-substituted Ci-Cisalkylamino or hydroxy-substituted di(Ci-Cisalkyl)amino, -0-(CH2)yNR15R16, or -0-(CH2)yNHR15Ri6H+A--, N-(CH2)yNR15R16 (CH2)yNHR15R16 Arr, wherein An- is an anion of a monovalent organic, or inorganic acid;
y is an integer from 2t0 10;
R15 is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, Rie is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, Me is a monovalent metal atom or the ammonium ion.
Z is oxygen or sulfur.

The second step ii) is preferably a transesterification reaction.
In step ii) the alcohol is preferably an ethoxylate of formula 5 RA-[0-CH2-CH2-]ni-OH (A), wherein RA is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, or alkylaryl or dialkylaryl with up to 24 carbon atoms and n1 is 1 to 150.
Preferably, step il) or i2) is carried out twice and a block copolymer is obtained wherein in 10 the first or second radical polymerization step the monomer or monomer mixture contains 50 to 100% by weight, based on total monomers, of a Cl-C6alkyl ester of acrylic or methacrylic acid and in the second or first radical polymerization step respectively, the ethylenically unsaturated monomer or monomer mixture contains at least a monomer without primary or secondary ester bond.
In the first polymerization step the monomer or monomer mixture contains from 50 to 100%
by weight based on total monomers of a Cl-C6alkyl ester of acrylic or methacrylic acid (first monomer) and in the second polymerization step the ethylenically unsaturated monomer or monomer mixture comprises 4-vinyl-pyridine or pyridinium-ion, 2-vinyl-pyridine or pyridinium-ion, vinyl-imidazole or imidazolinium-ion, 3-dimethylaminoethylacrylamide, 3-dimethylaminoethylmethacrylamide, or corresponding ammonium ion, 3-dimethylaminopropylacrylamide, or corresponding ammonium ion, or 3-dimethylaminopropylmethacrylannide, or corresponding ammonium ion (second monomer).

The nitroxylether is preferably a compound of formula (01).
The surface stabilization agent is preferably a copolymer which can be obtained by a process comprising the steps il) polymerizing in a first step a first monomer, which is a C1-C6 alkyl or hydroxy C1-C6 alkyl ester of acrylic or methacrylic acid, and a second monomer which is selected from selected from 4-vinyl-pyridine or pyridinium-ion, 2-vinyl-pyridine or pyridinium-ion, 1-vinyl-imidazole or imidazolinium-ion, 3-dimethylaminoethylacrylamide, 3-dimethylaminoethylmethacrylamide 3-dimethylaminopropylacrylamide, and 3-dimethylaminopropylmethacrylamide; in the presence of at least one nitroxylether having the structural element ; and ii) a second step, comprising the modification of the polymer or copolymer prepared under i) or ii) by a transesterification reaction, wherein the alcohol in step ii) is an ethoxylate of formula RA-[0-CH2-CH2-]ni-OH (A), wherein RA is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, or alkylaryl or dialkylaryl with up to 24 carbon atoms and n1 is 1 to 150.
Copolymers represented by formula Ra Ra. R13 R11 _ R12 - n Rb 0 Rb.0 (III) are preferred, wherein R11 and R12 are H or methyl, R13, Ra and Ra' are independently of each other H or methyl, Rb is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, RID' is RA-[0-CH2-CH2-]-0-0-, N+
is %H+ An -An ¨/ ¨/

An-N+ _____________________ , -C(=0)-N-(CH2)yNR15R'6, or -C(=0)-N-(CH2)yNHR15R16+An-, wherein An- is an anion of a monovalent organic, or inorganic acid;
y is an integer from 2t0 10;
R15 is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, R16 is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, RA is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, or alkylaryl or dialkylaryl with up to 24 carbon atoms and n1 is 1 to 150, m, n and p are independently of each other integers from 1 to 200, and o is an integer from 1 to 150.
Copolymers represented by formula R11 R12 _ 00oo (111) are more preferred, where R11 and R12 are H or methyl, m, n and p are independently of each other integers from 1 to 200, o is an integer from 1 to 150, especially an integer from 1 to 149. The order of monomers with indices m and n may be fixed (block copolymers) or not fixed (random copolymers).
Examples of preferred copolymers are the copolymers described in Example A3 (0-1), Example A6 (D-2) of W0200674969.
In addition to the surface stabilizing agents the composition may comprise further stabilizing agents. Stabilizing agents may include, for example, phosphines; phosphine oxides; alkyl phosphoric acids; oligoamines, such as ethylenediamine, diethylene triamine, triethylene tetramine, spermidine, spermine; compounds of formula (11a), (11b), (11c) and (11d) described below; surfactants; dendrimers, and salts and combinations thereof.
Surfactants include, for example, anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric or zwitterionic surfactants.
Anionic surfactants include, for example, alkyl sulfates (eg., dodecylsulfate), alkylamide sulfates, fatty alcohol sulfates, secondary alkyl sulfates, paraffin sulfonates, alkyl ether sulfates, alkylpolyglycol ether sulfates, fatty alcohol ether sulfates, alkylbenzenesulfonates, alkylphenol ether sulfates, alkyl phosphates; alkyl or alkylaryl monoesters, diesters, and triesters of phosphoric acid; alkyl ether phosphates, alkoxylated fatty alcohol esters of phosphoric acid, alkylpolyglycol ether phosphates (for example, polyoxyethylene octadecenyl ether phosphates marketed as LUBRHOPHOS(R) LB-400 by Rhodia), phosphoric esters, sulfosuccinic diesters, sulfosuccinic monoesters, alkoxylated sulfosuccinic monoesters, sulfosuccinim ides, a-olefinsulfonates, alkyl carboxylates, alkyl ether carboxylates, alkyl-polyglycol carboxylates, fatty acid isethionate, fatty acid methyltauride, fatty acid sarcoside, alkyl sulfonates (eg., 2-(methyloleoylamino)ethane-1-sulfonate, marketed as GEROPON(R) T77 by Solvay) alkyl ester sulfonates, arylsulfonates (eg., diphenyl oxide sulfonate, marketed as RHODACAL(R) DSB by Rhodia), naphthalenesulfonates, alkyl glyceryl ether sulfonates, polyacrylates, a-sulfa-fatty acid esters, and salts and mixtures thereof.
Cationic surfactants include, for example, aliphatic, cycloaliphatic or aromatic primary, secondary and tertiary ammonium salts or alkanolammonium salts; quaternary ammonium salts, such as tetraoctylammonium halides and cetyltrimethylammonium halides (eg., cetyltrimethylammonium bromide (CTAB)); pyridinium salts, oxazolium salts, thiazolium salts, salts of amine oxides, sulfonium salts, quinolinium salts, isoquinolinium salts, tropylium salts.
Other cationic surfactants suitable for use according to the present disclosure include cationic ethoxylated fatty amines. Examples of cationic ethoxylated fatty amines include, but are not limited to, ethoxylated ley! amine (marketed as RHODAMEEN PN-430 by Solvay), hydrogenated tallow amine ethoxylate, and tallow amine ethoxylate.
Nonionic surfactants include, for example, alcohol alkoxylates (for example, ethoxylated propoxylated C8-C10 alcohols marketed as ANTAROX BL-225 and ethoxylated propoxylated 010-C16 alcohols marketed as ANTAROX(R) RA-40 by Rhodia), fatty alcohol polyglycol ethers, fatty acid alkoxylates, fatty acid polyglycol esters, glyceride monoalkoxylates, alkanolamides, fatty acid alkylolamides, alkoxylated alkanol-amides, fatty acid alkylolamido alkoxylates, imidazolines, ethylene oxide-propylene oxide block copolymers (for example, EO/PO block copolymer marketed as ANTAROX L-64 by Rhodia), alkylphenol alkoxylates (for example, ethoxylated nonylphenol marketed as IGEPAL 00-630 and ethoxylated dinonylphenol/nonylphenol marketed as IGEPAL
DM-530 by Rhodia), alkyl glucosides, alkoxylated sorbitan esters (for example, ethoxylated sobitan monooleate marketed as ALKAMULS PSMO by Rhodia), alkyl thio alkoxylates (for example, alkyl thio ethoxylates marketed as ALCODET(R) by Rhodia), amine alkoxylates, and mixtures thereof.
Typically, nonionic surfactants include addition products of ethylene oxide, propylene oxide, styrene oxide, and/or butylene oxide onto compounds having an acidic hydrogen atom, such as, for example, fatty alcohols, alkylphenols or alcohols. Examples are addition products of ethylene oxide and/or propylene oxide onto linear or branched fatty alcohols having from 1 to 35 carbon atoms, onto fatty acids having from 6 to 30 carbon atoms and onto alkylphenols having from 4 to 35 carbon atoms in the alkyl group; (Co-C30)-fatty acid monoesters and diesters of addition products of ethylene oxide and/or propylene oxide onto glycerol; glycerol monoesters and diesters and sorbitan monoesters, diesters and triesters of saturated and unsaturated fatty acids having from 6 to 22 carbon atoms and their ethylene oxide and/or propylene oxide addition products, and the corresponding polyglycerol-based compounds; and alkyl monoglycosides and oligoglycosides having from 8 to 22 carbon atoms in the alkyl radical and their ethoxylated or propoxylated analogues.
Amphoteric or zwitterionic surfactants include, but are not limited to, aliphatic quaternary ammonium, phosphonium, and sulfonium compounds, wherein the aliphatic radicals can be straight chain or branched, and wherein the aliphatic substituents contains about 6 to about 30 carbon atoms and at least one aliphatic substituent contains an anionic functional group, such as carboxy, sulfonate, sulfate, phosphate, phosphonate, and salts and mixtures thereof. Examples of zwitterionic surfactants include, but are not limited to, alkyl betaines, alkyl amidopropyl betaines, alkyl sulphobetaines, alkyl glycinates, alkyl carboxyglycinates;
alkyl amphopropionates, such as cocoamphopropionate and caprylamphodipropionate (marketed as MIRANOL JBS by Rhodia); alkyl amidopropyl hydroxysultaines, acyl taurates, and acyl glutamates, wherein the alkyl and acyl groups have from 6 to 18 carbon atoms, and salts and mixtures thereof.
The stabilizing agent may be a compound of formula R20¨X (11a), wherein 1:129 is a linear or branched C1-C25alkyl group, or C1-C25alkenyI group, which may be substituted by one, or more groups selected from -OH, -SH, -NH2, or ¨000R19, wherein R19 is a hydrogen atom, or a Ci-C25alkyl group, and X is -OH, -SH, -N1-12, or ¨COOR19', wherein R19' is a hydrogen atom, a C1-025alkyl group, or a C2-C25alkenyl group, which may be substituted by one, or more groups selected from -OH, -SH, -NH2, or ¨0001919-, wherein R19- is a hydrogen atom, or a C1-C25alkyl group.
Examples of compounds of formula (11a) are 1-methylamine, 1-dodecylamine, 1-hexadecylamine, citric acid, oleic acid, D-cysteine, 1-dodecanethiol, 9-mercapto-1-nonanol, 1-thioglycerol, 11-amino-1 -undecanethiol, cysteamine, 3-mercaptopropanoic acid, 8-nnercaptooctanoic acid and 1,2-ethanedithiol.
The stabilizing agent may be a compound of formula R21 b R21 a N\
(11b), wherein R21a is a hydrogen atom, a halogen atom, a Cl-Csalkoxy group, or a Cl-Csalkyl group, R2113 is a hydrogen atom, or a group of formula -CHR24_N(R22)(R23), R22 and R23 are independently of each other a C1-C8alkyl, a hydroxyCi-Csalkyl group, or a group of formula -RCH2CH2)-01ni-CH2CH2-0H, wherein n1 is 1 to 5, R24 is H or Cl-Csalkyl.
CH El Olt NN
N
Examples of compounds of formula (11b) are (B-1), (B-2), r---\ OH r-\O H
CH3 r-NO H NO H
N //N
(B-3), (B-4), oH r---N__0 H
N N
er \¨\0 H CH3 r \¨\0 H
lN\ N N\
N" ,N i N4/
(B-5), (B-6) and ,........NI

N
\
Ni (B-7).
In another preferred embodiment the stabilizing agent is a "polyhydric phenol", which is a 5 compound, containing an optionally substituted benzene ring and at least 2 hydroxy groups attached to it. The term "polyhydric phenol" comprises polyphenols, such as, for example, tannic acid and polycyclic aromatic hydrocarbons which consist of fused benzene rings, wherein at least one benzene ring has at least 2 hydroxy groups attached to it, such as, for example, 1,2-dihydroxynaphthalene. The "polyhydric phenol" may be substituted.
Suitable 10 substituents are described below.
(OH)m3 or.(R25)n3 The polyhydric phenol is preferably a compound of formula (11c), wherein R25 can be the same, or different in each occurrence and is a hydrogen atom, a halogen atom, a C1-C18alkyl group, a C1-C18alkoxy group, or a group -C(=0)-R26, R26 is a hydrogen atom, a hydroxy group, a C1-C18alkyl group, unsubstituted or substituted

15 amino group, unsubstituted or substituted phenyl group, or a Ci-Cisalkoxy group, and n3 is a number of 1 to 4, m3 is a number of 2 to 4, and the sum of m3 and n3 is 6.
(01-1)fl13 R25b The polyhydric phenol is more preferably a compound of formula 20 (1Ic'), wherein R25 and R25b are independently of each other a hydrogen atom, a Ci-Cisalkyl group, a Ci-Cisalkoxy group, or a group of formula-C(=0)-R26, R26 is a hydrogen atom, a hydroxy group, a Ci-Cisalkyl group, an unsubstituted or substituted amino group, unsubstituted or substituted phenyl group, or a Ci-Clsalkoxy group, and m3 is a number of 2 to 4, especially 2 to 3. Polyhydric phenols are preferred, which have two hydroxy groups in ortho-position.
OH
HO
OH
lill Even more preferably, the polyhydric phenol is a compound of formula rµ
(Ika), wherein R25 is a hydrogen atom, or a group of formula -C(=0)-R26, wherein R26 is a hydrogen atom, a 01-C18alkyl group, or a C1-C18alkoxy group, an unsubstituted or substituted amino group, especially a C1-C18alkyl group or C1-C8alkoxy group.

HO OH
Olt Most preferred, the polyhydric phenol is a compound of formula (1Ica'), wherein R26 is a hydrogen atom, a Cl-Cisalkyl group, or a Cl-Ciaalkoxy group, especially a .....õ...

Ci-Csalkoxy group, such as, for example, (methyl gallate, C-1), HO OH HO OH

,------0 0 ---_-------0 0 (ethyl gallate, C-2), (propyl gallate, C-3), OH OH
HO OH HO OH
411:1 I.
"LO 0 7----/-0 0 (isopropyl gallate, C-4) (butyl gallate, C-5), HO OH
Oki WO o (octyl HOOH

0 o gallate, C-6) and (lauryl gallate, C-7).
In another preferred embodiment of the present invention the polyhydric phenols are compounds of formula OH

1.1 OH HO = OH 4 ) OH
OH OH OH
or , wherein R25 is a hydrogen atom, a C1-C18alkyl group, or a group of formula-C(=0)-R26, wherein R26 is a hydrogen atom, a hydroxy group, a Ci-Cisalkyl group, or a Ci-Cisalkoxy group, an unsubstituted or substituted amino group, an unsubstituted or substituted phenyl group, especially a CI-HO
HO*
Cisalkyl group or Ci-Csalkoxy group, such as, for example, HO
(C-8) and HO
HO
(C-9).
An unsubstituted or substituted amino group is, for example, a group of formula -NR27R28, wherein R27 and R28 are independently of each other a hydrogen atom, a Cl-Cisalkyl group, a phenyl group, preferably a hydrogen atom, or a Cl-Cisalkyl group.

In a particularly preferred embodiment the stabilizing agent is selected from compounds of formula (11b), (11c), or mixtures thereof.
In a particularly preferred embodiment the silver nanoplatelets comprise one, or more surface stabilizing agents of formula (1) and one, or more surface stabilizing agents of formula (Ill). In addition, the silver nanoplatelets may comprise one, or more stabilizing agents of formula (11b).
The most preferred (surface) stabilizing agents (surface stabilizing agents and stabilizing agents), or combinations thereof are shown in the below table.
Compound Compound of Compound of Anion of of formula (1) formula (Ill) formula (11b) formula (XX) (HOCH2CH2)2NH2+, Nat, K+ and Cs + represent preferred cations for the dithiocarbamate anion E-1.
A process for producing the composition according to the present invention, comprising the silver nanoplatelets, comprises:
(a) preparing a solution (a) comprising a silver precursor, a compound of formula - -H
R3 R4 R7 0 - k4 (r), wherein R1 is H, Cl-Cisalkyl, phenyl, Cl-Csalkylphenyl, or CH2COOH;
R2, R3, R4, R5, R6 and R7 are independently of each other H, Cl-Csalkyl, or phenyl;
Y is 0, or NR8;
R8 is H, or C1-C8alkyl;
k1 is an integer in the range of from 1 to 500, k2 and k3 are independently of each other 0, or integers in the range of from 1 to 250;
k4 is 0, or 1, k5 is an integer in the range of from 1 to 5;
and a polymer, or copolymer which can be obtained by a process comprising the steps i1) polymerizing in a first step one or more ethylenically unsaturated monomers in the \
presence of at least one nitroxylether having the structural element N¨O¨X
, /
wherein X represents a group having at least one carbon atom and is such that the free radical X. derived from X is capable of initiating polymerization; or i2) polymerizing in a first step one or more ethylenically unsaturated monomers in the \
presence of at least one stable free nitroxyl radical N¨Os and a free radical initiator;
/

wherein at least one monomer used in the steps i1) or i2) is a C1-06 alkyl or hydroxy C1-06 alkyl ester of acrylic or methacrylic acid; and optionally ii) a second step, comprising the modification of the polymer or copolymer prepared under il) or 12) by a transesterification reaction, an amidation, hydrolysis or anhydride modification or a combination thereof;
water, and optionally a defoamer;
(bl) preparing a solution (b), comprising a reducing agent, which comprises at least one boron atom in the molecule, and water;
(b2) adding solution (a) to solution (b), and adding one or more complexing agents;
(c) adding a hydrogen peroxide solution in water; and (d) optionally adding a stabilization agent to the mixture obtained in step (c), thereby synthesizing the composition, comprising the silver nanoplatelets.
The silver precursor is preferably a silver(I) compound, selected from the group consisting of AgNO3; AgC104; Ag2SO4; AgCI, AgF, Ag0H; Ag2O; AgBF4; Ag103; AgPF6;
R200CO2Ag, R2o0s03.
hkg wherein R2 is unsubstituted or substituted C1-C18alkyl, unsubstituted or substituted C5-C8cycloalkyl, unsubstituted or substituted C7-Ci8aralkyl, unsubstituted or substituted 06-C18aryl or unsubstituted or substituted 02-C18heteroaryl; Ag salts of dicarboxylic, tricarboxylic, polycarboxylic acids, polysulfonic acids, P-containing acids and mixtures thereof.
More preferably, the silver precursor is selected from the group consisting of silver nitrate, silver acetate, silver perch lorate, silver methanesulfonate, silver benzenesulfonate, silver toluenesulfonate silver trifluoromethanesulfonate, silver sulfate, silver fluoride and mixtures thereof. Silver nitrate is most preferred.
The reducing agent is selected from the group consisting of alkali, or alkaline earth metal borohydrides, such as sodium borohydride, alkali, or alkaline earth metal acyloxyborohydrides, such as sodium triacetoxyborohydride, alkali, or alkaline earth metal alkoxy- or aryloxyborohydrides, such as sodium trimethoxyborohydride, aryloxyboranes, such as catecholborane, and amine-borane complexes, such as diethylaniline borane, tert-butylamine borane, morpholine borane, dimethylamine borane, triethylamine borane, pyridine borane, ammonia borane and mixtures thereof. Sodium borohydride is most preferred.
The one or more complexing agents are selected from the group of chlor-containing compounds, which are capable to liberate chloride ions under reaction conditions, such as metal chlorides, alkyl or aryl ammonium chlorides, phosphonium chlorides;
primary or secondary amines and corresponding ammonium salts, such as methyl amine or dimethylamine; ammonia and corresponding ammonium salts; and aminocarboxylic acids and their salts, such as ethylenediaminetetraacetic acid.

Nonlimiting examples of complexing agents include ammonia, methylamine, dimethylamine, ethylamine, ethylenediamine, diethylenetriamine, ethylene-diamine-tetraacetic acid (EDTA);
ethylenediamine N,N'-disuccinic acid (EDDS); methyl glycine diacetic acid (MGDA);
diethylene triamine penta acetic acid (DTPA); propylene diamine tetracetic acid (PDT A);
glutamic acid N,N-diacetic acid (N,N-dicarboxymethyl glutamic acid tetrasodium salt (GLDA); nitrilotriacetic acid (NTA), and any salts thereof; N-hydroxyethylethylenediaminetri-acetic acid (HEDTA), triethylenetetraaminehexaacetic acid (TTHA), N-hydroxyethyliminodiacetic acid (HEIDA), dihydroxyethylglycine (DHEG), ethylenediaminetetrapropionic acid (EDTP) and derivatives thereof, such as, for example, trisodium salt of methylglycinediacetic acid (Na3MGDA) and tetrasodium salt of EDTA.
The defoamer is a compound or composition, capable to suppress foam formation in the reaction mixture, such as, for example, commercially available TEGO Foamex 1488, 1495, 3062, 7447, 800, 8030, 805, 8050, 810, 815N, 822, 825, 830, 835, 840, 842, 843, 845, 855, 860, 883, K 3, K 7, K 8, N, Antifoam SE-15 from Sigma, Struktol SB-2080 and the like. The amount of the defoamer is in the range of from 0.00001 % to 5% by weight based on total weight of reaction mixture prior to hydrogen peroxide addition, preferably from 0.0001 % to 3% and more preferably from 0.001 % to 2 % by weight.
The defoamer can be added to any of the solutions (a) and (b).
Preferably, the reaction of silver nanoplatelets formation is carried out at a total silver concentration of >1% w/w after combining the first solution with the second solution.
Preferably, the reaction of silver nanoplatelets formation is carried out by gradually adding the silver precursor solution into reducing agent solution, whereas the temperature of both solutions is in the range of -3 to 40 C and the gradual addition is completed within 15 minutes to 24 h time.
The silver nanoplatelets can be isolated by known methods such as decantation, filtration, (ultra)centrifugation, reversible or irreversible agglomeration, phase transfer with organic solvent and combinations thereof. The silver nanoplatelets may be obtained after isolation as a wet paste or dispersion in water. The silver nanoplatelets content in the final preparation of said particles may be up to about 99% by weight, based on the total weight of the preparation, preferably between 5 to 99% by weight, more preferably 5 to 90% by weight.
A preferred aspect of the present invention relates to a method which comprises further a step e), wherein the dithiocarbamate capped silver nanoplatelets are prepared i) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets; or ii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and a base; or iv) by reacting CS2 with an amine of formula R41 R42NH in the presence of a base to obtain a S - Catk+
compound of formula ¨ - k (XXI), which is then reacted with a composition of silver nanoplatelets; wherein R41 and R42 are defined above, or below, Catk+ is a cation and k is 1, or 2.
In case of ii) and iii) the base is preferably selected from alkali or alkaline earth metal hydroxides, alkali or alkaline earth metal alkoxides, amines and quaternary ammonium hydroxides and mixtures thereof.
In case of iv) the base is preferably selected from alkali or alkaline earth metal hydroxides, alkali or alkaline earth metal alkoxides and mixtures thereof. Preferred examples of bases are NaOH, KOH and Cs0H, NaOCH2CH3, KOCH2CH3, CsOCH2CH3, and mixtures thereof.
More preferably, the base is selected from alkali metal hydroxides, such as, for example, NaOH, KOH and Cs0H, alkali metal alkoxides, such as, for example, NaOCH2CH3, KOCH2CH3 and CsOCH2CH3, amines of formula R43R44R45N, especially (HOCH2CH2)2NH

and (HOCH2CH2)3N, and mixtures thereof.
With respect to the compound of formula (XXI) the same preferences apply for R41 and R42 as in case of formula (XX) and Catk+ is selected from alkali metal cations, alkaline earth metal cations and R43R44R45NH+, such as, for example, (HOCH2CH2)2NH2+ and (HOCH2CH2)3NH+, and mixtures thereof and is preferably selected from alkali metal cations, alkaline earth metal cations and mixtures thereof. Catk+ is more preferably selected from alkali metal cations, most preferred from Cs, Rb+, K+ and Na + and mixtures thereof.
Examples of compounds of formula (XXI) are compound (21b), (21b) and (21c).
Compounds (21a) and (21b) are more stable and are preferred.
In reaction sequences iv) it is preferred that the compound of formula (XXI) is reacted with the silver nanoplatelets immediately after preparation The in-situ synthesis of the dithiocarbamate anions in the presence of the silver nanoplatelets, i.e. reaction sequences i), ii) and iii) are more preferred.
5 In reaction sequence i) carbon disulfide or its solution in a solvent and an amine of formula R41R42NH or its solution in a solvent are successively added to an Ag nanoplatelets dispersion under inert gas atmosphere at 0-30 C. The reaction mixture is stirred for 5 minutes to 24 h at 0-300C.
10 In reaction sequence ii) carbon disulfide or its solution in a solvent and an amine of formula R41R42NH or its solution in a solvent are successively added to an Ag nanoplatelets dispersion under inert gas atmosphere at 0-30 C. The reaction mixture is stirred for 5 minutes to 24 h at 0-30 C and then a solution of a base, such as, for example, cesium hydroxide, potassium ethoxide or diethanolamine, in a solvent is added and the reaction 15 mixture is stirred for 5 min to 24 h at 0-300.
In reaction sequence iii) carbon disulfide or its solution in a solvent and a mixture of amine of formula R41R42NH and a base, such as, for example, cesium hydroxide, potassium ethoxide or diethanolamine, or their solution in a solvent, are successively added to an Ag 20 nanoplatelets dispersion under inert gas atmosphere at 0-30 C and the reaction mixture is stirred for 5 min to 24 h at 0-30'. The amine of formula R41R42NH and the base may also be added separately in parallel.
Examples of suitable solvents are water, ethanol, isopropanol, ethyl-3-ethoxypropionate and 25 1-methoxy-2-propanol, or mixtures thereof.
A preferred aspect of the present invention relates to a method which comprises further a step f), wherein the dispersion of the silver nanoplatelets is concentrated and/or water is replaced at least partially with an organic solvent. Examples of suitable organic solvents are 30 ethanol, isopropanol, ethyl acetate, ethyl-3-ethoxypropionate and 1-methoxy-2-propanol, or mixtures thereof, optionally with water.
The present application is also directed to compositions, comprising silver nanoplatelets, which are obtained by above-described process.
The compositions of the present invention may be used in coatings, or printing inks, which are described for example, in W02020/224982.
The suitability of dithiocarbamate capped silver nanoplatelets for use in security inks for producing security features for securing value documents, which exhibit a first color upon viewing in transmitted light and a second color different from the first color upon viewing in incident light is described in two European patent applications both entitled "UV-VIS

radiation curable security inks for producing dichroic security features"
filed by SICPA
HOLDING SA on November 10, 2020.
Part of the European patent applications of SICPA HOLDING SA is outlined below in excerpts for reference purpose only.
The 15t European patent application of SICPA HOLDING SA describes UV-VIS
radiation curable security inks, wherein said inks comprise:
a) from about 7.5 wt-% to about 20 wt-% of silver nanoplatelets having a mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy, and wherein the silver nanoplatelets bear a surface stabilizing agent of general formula S Catk+
¨ k (XXI), wherein the residue R41 is a C2-C4alkyl group substituted with a hydroxy group;
the residue R42 is selected from a C1-C4 alkyl group, and a C2-C4alkyl group substituted with a hydroxy group; and Catk+ is a cation selected from the group consisting of Nat, K-h, Rb-h and Cs-h;
b) a perfluoropolyether surfactant functionalized with at least a hydroxy group;
c) from about 3 wt-% to about 12 wt-% of a polyvinyl chloride copolymer containing at least 69 wt-% of vinyl chloride;
d) dl) from about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and from about 1 wt-% to about 10 wt-% of a cationic photoinitiator; or d2) from about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, from about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and from about 1 wt-% to about 6 wt-% of a free radical photoinitiator; and optionally e) a cationically curable compound selected from the group consisting of:
el) a vinyl ether having two vinyloxy residues in an amount lower than 50% of the weight percent (wt-%) of the cycloaliphatic epoxide of d);
e2) a vinyl ether having one vinyloxy residue in an amount lower than about 5 wt-%;
e3) an epoxide other than a cycloaliphatic epoxide in an amount lower than about 10 wt-%;
e4) an oxetane having two oxetanyl residues in an amount lower than about 20 wt-%;

e5) an oxetane having one oxetanyl residue in an amount lower than about 3.5 wt-%;
and e6) a mixture of el) and/or e2) and/or e3) and/or e4) and/or e5); the weight percents being based on the total weight of the UV-Vis radiation curable security ink;
and a process for producing a security feature for securing a value document, wherein said security feature exhibits a blue color upon viewing in transmitted light and a metallic yellow color upon viewing in incident light, said process comprising the following steps:
A) printing, preferably by screen printing, rotogravure, or flexography, the UV-Vis radiation curable security ink claimed and described herein on a transparent or partially transparent region of a substrate of a value document to provide an ink layer; and B) UV-Vis curing the ink layer obtained at step A) to form the security feature.
The combination of the ditiocarbamate capped silver nanoplatelets of the present invention and the specific ink vehicle described in the European patent application of SICPA
HOLDING SA allows expedient migration of the silver nanoplatelets contained in an ink layer obtained by printing the security ink from the mass of the ink layer at the interface between the ink layer and air and at the interface between the ink layer and the substrate and alignment at said interfaces to form thin reflective layers, thereby producing independently of the thickness of the printed ink layer the metallic yellow color in reflection and the blue color in transmission. The expedient development of the metallic yellow color in reflection and of the blue color in transmission cannot be achieved with the inks descried in the prior art. The cationically curable binder or hybrid curable binder contained by the UV-Vis radiation curable security ink provides the dichroic security feature obtained from said ink with a high mechanical resistance. The UV-Vis radiation curable ink described therein has outstanding shelf stability.
A UV-Vis radiation cationically curable security ink may comprise:
a) from about 7.5 wt-% to about 20 wt-% of silver nanoplatelets having a mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy, and wherein the silver nanoplatelets bear a surface stabilizing agent of general formula (I) s Catk+
Rs/
¨k (XXI), wherein the residue R41 is a C2-C4alkyl group substituted with a hydroxy group;
the residue R42 is selected from a Ci-04 alkyl group, and a 02-C4alkyl group substituted with a hydroxy group; and Catk+ is a cation selected from the group consisting of Na, K+, Rb+ and Cs;
b) a perfluoropolyether surfactant functionalized with at least a hydroxy group;
c) from about 3 wt-% to about 12 wt-% of a polyvinyl chloride copolymer containing at least 69 wt-% of vinyl chloride;
dl) from about 25 wt-% to about 55 wt-% of a cycloaliphatic epoxide, and from about 1 wt-% to about 10 wt-% of a cationic photoinitiator; and optionally e) a cationically curable compound selected from the group consisting of:
el) a vinyl ether having two vinyloxy residues in an amount lower than 50% of the weight percent (wt-%) of the cycloaliphatic epoxide of d);
e2) a vinyl ether having one vinyloxy residue in an amount lower than about 5 wt-%, preferably lower than or equal to about 4.1 wt-%;
e3) an epoxide other than a cycloaliphatic epoxide in an amount lower than about 10 wt-%;
e4) an oxetane having two oxetanyl residues in an amount lower than about 20 wt-%;
e5) an oxetane having one oxetanyl residue in an amount lower than about 3.5 wt-%, preferably lower than or equal to about 3.3 wt-%; and e6) a mixture of el) and/or e2) and/or e3) and/or e4) and/or e5); the weight percents being based on the total weight of the UV-Vis radiation curable security ink.
A UV-Vis radiation hybrid curable security ink may comprise:
a) from about 7.5 wt-% to about 20 wt-% of silver nanoplatelets having a mean diameter in the range of 50 to 150 nm with a standard deviation of less than 60%, a mean thickness in the range of 5 to 30 nm with a standard deviation of less than 50%, and a mean aspect ratio higher than 2.0, wherein the mean diameter is determined by transmission electron microscopy and the mean thickness is determined by transmission electron microscopy, and wherein the silver nanoplatelets bear a surface stabilizing agent of general formula S- Cat"
R41Ny ¨k (XXI), wherein the residue R4' is a C2-C4alkyl group substituted with a hydroxy group;
the residue R42 is selected from a C1-C4 alkyl group, and a C2-C4alkyl group substituted with a hydroxy group; and Cat k+ is a cation selected from the group consisting of Na, K+, Rb+ and Cs;
b) a perfluoropolyether surfactant functionalized with at least a hydroxy group;
C) from about 3 wt-% to about 12 wt-% of a polyvinyl chloride copolymer containing at least 69 wt-% of vinyl chloride;

d2) from about 30 wt-% to about 65 wt-% of a mixture of a cycloaliphatic epoxide and a radically curable compound, from about 1 wt-% to about 6 wt-% of a cationic photoinitiator, and from about 1 wt-% to about 6 wt-% of a free radical photoinitiator; and optionally e) a cationically curable compound selected from the group consisting of:
el) a vinyl ether having two vinyloxy residues in an amount lower than 50% of the weight percent (wt-%) of the cycloaliphatic epoxide of d);
e2) a vinyl ether having one vinyloxy residue in an amount lower than about 5 wt-%, preferably lower than or equal to about 4.1 wt-%;
e3) an epoxide other than a cycloaliphatic epoxide in an amount lower than about 10 wt- /0;
e4) an oxetane having two oxetanyl residues in an amount lower than about 20 wt-%;
e5) an oxetane having one oxetanyl residue in an amount lower than about 3.5 wt-%, preferably lower than or equal to about 3.3 wt-%; and e6) a mixture of el) and/or e2) and/or e3) and/or e4) and/or e5); the weight percents being based on the total weight of the UV-Vis radiation curable security ink.
The 2nd European patent application of SICPA HOLDING SA describes UV-VIS
radiation curable security inks, wherein Cat'- in formula (XXI) is an ammonium cation of general formula RcIRDNH2+, wherein the residue Fic is a 02-C4alkyl group substituted with a hydroxy group, and the residue RD is selected from a C1-C4alkyl group, or a 02-C4alkyl group substituted with a hydroxy group.
Further details of the security inks are described in the two European patent applications of SICPA HOLDING SA.
The following examples are intended to illustrate various aspects and features of the present invention.
Examples UV-Vis spectra of dispersions were recorded on Varian Cary 50 UV-Visible spectrophotometer at such concentration of dispersions as to achieve the optical density of 0.3 to 1.5 at 1 cm optical path.
TEM analysis was conducted on dispersions containing silver nanoplatelets in isopropanol using an EM 910 instrument from ZEISS, INST.109, in bright field mode at an e-beam acceleration voltage of 100kV. At least 2 representative images with scale in different magnification (5.000x, 10.000X and 20.000X) were recorded in order to characterize the dominant particle morphology for each sample.
The "number mean diameter of the silver nanoplatelets" refers to the mean diameter determined by transmission electron microscopy (TEM) using Fiji image analysis software (or Image analysis software: ParticleSizer (Thorsten Wagner (2016) ij-particlesizer:

ParticleSizer 1Ø9. Zenodo; 10.5281/zen0do.820296) and ImageJ version 1.53f51) based on the measurement of at least 300, especially at least 500 randomly selected silver nanoplatelets oriented parallel to the plane of a transmission electron microscopy image (TEM), wherein the diameter of a silver nanoplatelet is the maximum dimension of said 5 silver nanoplatelet (maximal Feret diameter) oriented parallel to the plane of a transmission electron microscopy (TEM) image (recorded at magnification 20.000X).
The "number mean thickness of silver nanoplatelets" refers to the mean thickness determined by transmission electron microscopy (TEM) based on the measurement of at 10 least 50, especially of at least 300 randomly selected silver nanoplatelets oriented perpendicular to the plane of the TEM image (recorded at magnification 25.000X), wherein the thickness of the silver nanoplatelet is the maximum thickness of said silver nanoplatelet.
TEM analysis was conducted on dispersions containing silver nanoplatelets in isopropanol using an EM 910 instrument from ZEISS, INST.109, in bright field mode at an e-beam 15 acceleration voltage of 100kV.
In detail, a part of the dispersion is transferred to a smooth foil. After drying the sample is embedded in Araldit , which is cross-linked below 60 C. Ultrathin cross-sections of the embedded sample are prepared perpendicular to the foil surface. The thickness of at least 20 300 randomly selected silver nanoplatelets may be determined from the cross-sectional TEM images (recorded at magnification 25.000X) by fitting ellipses to the cross-sectioned particles by the software (ParticleSizer). The minor axis (the shortest diameter) of the fitted ellipse is taken as particle thickness.
25 Synthesis Example 1 (see Example 1 of W02020/224982) a) In a 1 L double-wall glass reactor, equipped with anchor-stirrer, 365 g of de-ionized water was cooled to +2 C. 13.62 g of sodium borohydride was added, and the mixture was cooled to -1 C with stirring at 250 rounds per minute (RPM, Solution A).
In a 0.5 L double-wall glass reactor, equipped with anchor-stirrer, 132 g of deionized water 30 and 4.8 g of MPEG-5000-thiol were combined, and the mixture was stirred for 10 minutes at room temperature. 72 g of the product of Example A3 of W02006074969 was added, and the resulting mixture was stirred for another 10 minutes at room temperature for homogenization. The solution of 30.6 g of silver nitrate in 30 g of de-ionized water was added in one portion and the mixture was stirred for 10 minutes, resulting in an orange-35 brown viscous solution. To this solution 96 g of deionized water was added, followed by addition of 3 g of Struktol SB2080 defoamer, pre-dispersed in 36 g of de-ionized water. The resulting mixture was cooled to 0 C with stirring at 250 RPM (Solution B).
After that, Solution B was dosed with a peristaltic pump at a constant rate over 2 h into Solution A under the liquid surface via a cooled (0 C) dosing tube, resulting in spherical silver nanoplatelets dispersion. During pumping, the Solution A was stirred at 250 RPM.
After dosing was complete, the reaction mixture was warmed up to +5 C within 15 minutes, and a solution of 862 mg of KCI in 10 g of deionized water was added in one portion, followed by addition of 9.6 g of ethylenediaminetetraacetic acid (EDTA) in 4 equal portions with 10 minutes time intervals.
After addition of the last EDTA portion, the reaction mixture was stirred for 15 minutes at +5 C, then warmed up to 35 C over 30 minutes and stirred for 1 h at this temperature. Upon this time, hydrogen evolution is completed.
3.0 mL of 30% w/w solution of ammonia in water was added, followed by addition of 5.76 g of solid NaOH, and the mixture was stirred for 15 min at 35 C. Then 180 mL of 50% w/w hydrogen peroxide solution in water were dosed with a peristaltic pump at a constant rate over 4 h into the reaction mixture under the liquid surface with stirring at 250 RPM, while maintaining the temperature at 35 C. This has led to a deep blue colored dispersion of silver nanoplatelets, which was cooled to room temperature. 1.23 g of compound of formula OH
CH3 r-N

(B-3) was added, and the mixture was stirred for 1 h at room temperature.
b) Isolation and purification of Ag nanoplatelets bl) Decantation 9.6 g of sodium dodecylsulfate was added to the reaction mixture and then ca.
25 g of anhydrous sodium sulfate powder was added in portions with stirring until the transmission color of the dispersion changed from blue to pink. Then the mixture was kept without stirring at room temperature for 24 h, allowing the coagulated nanoplatelets to sediment at the bottom of the reactor.
890 g of supernatant was pumped out from the reactor with a peristaltic pump, and 890 g of deionized water was added to the reactor. The mixture in reactor was stirred for 1 h at room temperature, allowing the coagulated particles to re-disperse.
b2) Decantation Ca. 64 g of anhydrous sodium sulfate powder was added in portions with stirring until the transmission color of the dispersion changed from blue to yellowish-pink. Then the mixture was kept without stirring at room temperature for 12 h, allowing the coagulated nanoplatelets to sediment at the bottom of the reactor. 990 g of supernatant was pumped out from the reactor with a peristaltic pump, and 90 g of deionized water was added to the reactor. The resulting mixture was stirred for 30 minutes at room temperature, allowing the coagulated particles to re-disperse.
b3) Ultrafiltration in water The resulting dispersion of Ag nanoplatelets was subjected to ultrafiltration using a Millipore Amicon 8400 stirred ultrafiltration cell. The dispersion was diluted to 400 g weight with de-ionized water and ultrafiltered to the end volume of ca. 50 mL using a polyethersulfone (PES) membrane with 300 kDa cut-off value. The procedure was repeated in total 4 times to provide 60 g of Ag nanoplatelets dispersion in water. After ultrafiltration was completed, 0.17 g of compound (B-3) was added to the dispersion.
Ag content 28.9% w/w; yield ca. 89% based on total silver amount; Solids content (at 250 C) 33.5% w/w; Purity 86% w/w of silver based on solids content at 250 C.
b4) Ultrafiltration in isopropanol The dispersion was further ultrafiltered in isopropanol. 60 g of Ag nanoplatelets dispersion, obtained after ultrafiltration in water, was placed in a Millipore Amicon 8400 stirred ultrafiltration cell and diluted to 300 g weight with isopropanol. The dispersion was ultrafiltered to the volume of ca. 50 mL using a polyethersulfone (PES) membrane with 500 kDa cut-off value. The procedure was repeated in total 4 times to provide 72 g of Ag nanoplatelets dispersion in isopropanol.
Ag content 24.1% w/w; Solids content (at 250 C) 25.7% w/w; Purity 93.5% w/w of silver based on solids content at 250 C.
The UV-Vis-NIR spectrum was recorded in water at Ag concentration of 9.8*10-5 M. Amax =
700 nm; extinction coefficient at maximum E=10200 L/(cm*mol Ag), FWHM = 340 nm.
Reference is made to Fig. 1. UV-Vis-NIR spectrum of Ag nanoplatelets from Example 1 b4).
Number mean particle diameter 93 40 nm, number mean particle thickness 16 2.5 nm.
Example 1. Preparation of Dispersion Dl. Pre-synthesis of diethanolaminedithiocarbamate sodium salt. Dispersion in ethyl 3-ethoxypropionate a) Synthesis of diethanolaminedithiocarbamate sodium salt (sodium bis(2-hydroxyethyl)dithiocarbamate) 60 g Ethanol, 10.5 g diethanolamine and 4.0 g of sodium hydroxide granules was placed in 100 mL round-bottom flask under argon atmosphere, the mixture was stirred until dissolution of sodium hydroxide and then cooled to +2 C. 7.6 g carbon disulfide was added dropwise over 1 h with stirring, maintaining the temperature of reaction mixture at 0 to +5 C.
After that, the mixture (yellowish suspension) was stirred for 30 min at 0 to +5 C, then warmed up to 23 C and stirred for 1 h.
b) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion obtained as described in Step b4) of Synthesis Example 1 was placed in a 250 mL round-bottom flask under argon atmosphere.
1.09 g of suspension (0.27 g of diethanolaminedithiocarbamate sodium salt), obtained in Step a), was added in one portion and the mixture was stirred for 24 h under argon at 23 C.
c) Solvent switch To the dispersion, obtained in Step b), 15.0 g of ethyl 3-ethoxypropionate (CAS No.: 763-69-9) was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off.
The weight of the resulting dispersion was adjusted to 32.1 g by addition of ethyl 3-ethoxypropionate (corresponds to the calculated total solids content of 40.9% w/w).

Example 2. Preparation of Dispersion 02. In-situ synthesis of diethanolaminedithiocarbamate potassium salt. Dispersion in ethyl 3-ethoxypropionate a) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion, obtained as described in Step b4) of Synthesis Example 1, was placed in a 250 mL round-bottom flask under argon atmosphere at 23 C. 0.91 g of 5% w/w solution of carbon disulfide in absolute ethanol was added and the mixture was stirred for 5 min, followed by addition of 1.24 g of 5% w/w solution of diethanolamine in absolute ethanol. The mixture was stirred for 1 h at 23 C, then 0.986 g of 5% w/w solution of potassium ethoxide in absolute ethanol was added and stirring was continued for 30 min.
b) Solvent switch To the dispersion, obtained in Step a), 15.0 g of ethyl 3-ethoxypropionate was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of ethyl 3-ethoxypropionate (corresponds to the calculated total solids content of 40.4% w/w).
Example 3. Preparation of Dispersion D3. Pre-synthesis of diethanolaminedithiocarbamate cesium salt. Dispersion in ethyl 3-ethoxypropionate a) Synthesis of diethanolaminedithiocarbamate cesium salt

16 g Ethanol, 2.7 g diethanolamine and 4.3 g of cesium hydroxide monohydrate was placed in 100 mL round-bottom flask under argon atmosphere, the mixture was stirred until dissolution of cesium hydroxide and then cooled to +2 C. 1.95 g carbon disulfide was added dropwise over 1 h with stirring, maintaining the temperature of reaction mixture at 0 to +5 C.
After that, the mixture (yellowish suspension) was stirred for 30 min at 0 to +5 C, then warmed up to 23 C and stirred for 1 h.
b) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion, obtained obtained in Example 1, Step b4) of the European patent application 19172734.6, was placed in a 250 mL
round-bottom flask under argon atmosphere. 0.40 g of suspension (0.128 g of diethanolaminedithiocarbamate cesium salt), obtained in Step a), was added in one portion and the mixture was stirred for 24 h under argon at 23 C.
c) Solvent switch To the dispersion, obtained in Step b), 15.0 g of ethyl 3-ethoxypropionate was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of ethyl 3-ethoxypropionate (corresponds to the calculated total solids content of 40.4% w/w).

Example 4. Preparation of Dispersion 04. In-situ synthesis of diethanolaminedithiocarbamate potassium salt. Dispersion in 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate.
a) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion, obtained as described in Step b4) of Synthesis Example 1, was placed in a 250 mL round-bottom flask under argon atmosphere at 23 C. 0.91 g of 5% w/w solution of carbon disulfide in absolute ethanol was added and the mixture was stirred for 5 min, followed by addition of 1.24 g of 5% w/w solution of diethanolamine in absolute ethanol. The mixture was stirred for 1 h at 23 C, then 0.986 g of 5% w/w solution of potassium ethoxide in absolute ethanol was added and stirring was continued for 30 min.
b) Solvent switch To the dispersion, obtained in Step a), 15.0 g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (CAS: 2386-87-0) was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (corresponds to the calculated total solids content of 40.4% w/w).
Example 5. Preparation of Dispersion 05. In-situ synthesis of diethanolaminedithiocarbamate cesium salt. Dispersion in 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate a) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion, obtained as described in Step b4) of Synthesis Example 1, was placed in a 250 mL round-bottom flask under argon atmosphere at 23 C. 0.91 g of 5% w/w solution of carbon disulfide in absolute ethanol was added and the mixture was stirred for 5 min, followed by addition of 1.24 g of 5% w/w solution of diethanolamine in absolute ethanol. The mixture was stirred for 1 h at 23 C, then 1.97 g of 5% w/w solution of cesium hydroxide monohydrate in absolute ethanol was added and stirring was continued for 30 min.
b) Solvent switch To the dispersion, obtained in Step a), 15.0 g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (CAS: 2386-87-0) was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (corresponds to the calculated total solids content of 40.6% w/w).
Example 6. Preparation of Dispersion D6. In-situ synthesis of diethanolaminedithiocarbamate diethanolammonium salt. Dispersion in ethyl 3-ethoxypropionate a) Surface modification of Ag nanoplatelets 50 g (12.85 g solids) of Ag nanoplatelets dispersion, obtained as described in Step b4) of Synthesis Example 1, was placed in a 250 mL round-bottom flask under argon atmosphere at 23 C. 2.05 g of 5% w/w solution of carbon disulfide in absolute ethanol was added and the mixture was stirred for 5 min, followed by addition of 2.77 g of 5% w/w solution of 5 diethanolamine in absolute ethanol. The mixture was stirred for 1 h at 23 C, then 2.77 g of 5% w/w solution of diethanolamine in absolute ethanol was added and stirring was continued for 30 min.
b) Solvent switch To the dispersion, obtained in Step a), 15.0 g of ethyl 3-ethoxypropionate was added. The 10 resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of ethyl 3-ethoxypropionate (corresponds to the calculated total solids content of 41.2% w/w).
15 Example 7. Preparation of Dispersion 07. In-situ synthesis of diethanolaminedithiocarbamate diethanolammonium salt. Dispersion in 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate a) Surface modification of Ag nanoplatelets g (12.85 g solids) of Ag nanoplatelets dispersion, obtained as described in Step b4) of 20 Synthesis Example 1, was placed in a 250 mL round-bottom flask under argon atmosphere at 23 C. 2.05 g of 5% w/w solution of carbon disulfide in absolute ethanol was added and the mixture was stirred for 5 min, followed by addition of 2.77 g of 5% w/w solution of diethanolamine in absolute ethanol. The mixture was stirred for 1 h at 23 C, then 2.77 g of 5% w/w solution of diethanolamine in absolute ethanol was added and stirring was 25 continued for 30 min.
b) Solvent switch To the dispersion, obtained in Step a), 15.0 g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (CAS: 2386-87-0) was added. The resulting mixture was concentrated on rotary evaporator at 40 mbar pressure and 40 C bath temperature, till no 30 more solvent was distilled off. The weight of the resulting dispersion was adjusted to 32.1 g by addition of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (corresponds to the calculated total solids content of 41.2% w/w).
The suitability of dithiocarbamate capped silver nanoplatelets for use in security inks for 35 producing security features for securing value documents, which exhibit a first color upon viewing in transmitted light and a second color different from the first color upon viewing in incident light is described in two European patent applications both entitled "UV-VIS
radiation curable security inks for producing dichroic security features"
filed by SICPA
HOLDING SA on November 10, 2020.
Part of the examples of the European patent applications of SICPA HOLDING SA
are outlined below in excerpts for reference purpose only.

The examples El ¨ E8 and below provide more details for the preparation the UV-Vis radiation curable screen printing security inks described in the European patent applications of SICPA
HOLDING SA and optical properties of security features obtained therefrom.

LO
A. Preparation of Examples (El ¨ E8) and printed security features thereof Description of the ingredients used for the preparation of the inks according to the present invention (El ¨ E8) Table la. Ingredients Commercial name Chemical composition Ingredient (supplier) (CAS
number) Polyvinylchloride Vinnol H14/36 85.6wt- /0 PVC + 14.4wt- /0 PVAc (9003-22-9) copolymer (Wacker) Cycloaliphatic Uvacure 1500 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (2386-87-0) epoxide (Allnex) CHDM-di (BASF) 1,4-bis[(vinyloxy)methyl]cyclohexane (17351-75-6) Vinyl ether DVE-3 (BASF) triethylenegylcol divinylether (765-12-8) 23wt- /0 glycerol, propoxylated, esters with acrylic acid (52408-84-1) + 77wt-% 4,4'-Ebecryl 2959 Isopropylidene Acrylate oligomer (Allnex) diphenol, oligomeric reaction products with 1-chloro-2,3-epoxypropane, esters with acrylic acid (55818-57-0) Acrylate monomer TMPTA (Allnex) 2,2-bis(acryloyloxymethyl)butyl acrylate (15625-89-5) Perfluoropolyether Fluor Mk El OH Tetrafluoroethylene, oxidized, oligomers, reduced, methyl esters, reduced, reaction products reactive surfactant (Solvay) with ethylene oxide (162492-15-1); Average molecular weight 1700 [g/mol]
50wt- /0 mixture of Sulfonium, diphenyl[4-(phenylthio)phenyl]-, (0C-6-11)-Speedcure 976 hexafluoroantimonate(1-) (1:1) +
Sulfonium, (thiodi-4,1-phenylene)bis[diphenyl-, (00-6-11)-(Lambson) hexafluoroantimonate(1-) (1:2) (71449-78-0 and 89452-37-9) in 50% propylene carbonate (108-Cationic 32-7) -o photoinitiator 35wt-% mixture of Sulfonium, diphenyl[4-(phenylthio)phenyl]-, (00-6-11)- 7,1 Speedcure 976D hexafluoroantimonate(1-) (1:1) +
Sulfonium, (thiodi-4,1-phenylene)bis[diphenyl-, (00-6-11)- "0 (Lambson) hexafluoroantimonate(1-) (1:2) (71449-78-0 and 89452-37-9) in 65wt-% Oxirane, 2,2'-[1,4-butanediyIbis(oxymethylene)]bis- (2425-79-8) Radical Omnirad 2100 92.5% ethyl pheny1(2,4,6-trimethylbenzoyl)phosphinate + 7.5wt-% phenyl bis(2,4,6-photoinitiator (IGM Resins) trimethylbenzoyI)-phosphine oxide (448-61-3) LO
Amount surface stabilizing agent (wt-% of the Surface stabilizing agent Ag nanoplatelets) Dispersion D1 a) Diethanolamine dithiocarbamate sodium salt 2.1 (sodium bis(2-hydroxyethyl)dithiocarbamate) Dispersion D2 b) Diethanolamine dithiocarbamate potassium salt 1.0 (potassium bis(2-hydroxyethyl)dithiocarbamate) Dispersion D3 c) Diethanolamine dithiccarbamate cesium salt Dispersion Ag 1.0 (cesium bis(2-hydroxyethyl)dithiocarbamate) nanoplatelets Dispersion D4 d) Diethanolamine dithiocarbamate potassium salt 1.0 (potassium bis(2-hydroxyethyl)dithiocarbamate) Dispersion D5 e) Diethanolamine dithiccarbamate cesium salt 1.43 (cesium bis(2-hydroxyethyl)dithiocarbamate) diethanolammonium dihydroxyethyldithio-Dispersion D6 f) carbamate diethanolammonium dihydroxyethyldithio-Dispersion D7 g) carbamate a) 40.9 wt-% Ag nanoplatelets stabilized with sodium bis(2-hydroxyethyl)dithiocarbamate in ethyl-3-ethoxypropionate (763-69-9) b) 40.4 wt-% Ag nanoplatelets stabilized with potassium bis(2-hydroxyethyl)dithiocarbamate in ethy1-3-ethoxypropionate (763-69-9) 0 40.4 wt-% Ag nanoplatelets stabilized with cesium bis(2-hydroxyethyl)dithiocarbamate in ethyl-3-ethoxypropionate (763-69-9) cl) 40.4 wt-% Ag nanoplatelets stabilized with potassium bis(2-hydroxyethyl)dithiocarbamate in 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (Uvacure 1500; CAS number: 2386-87-0) a) 40.6 wt-% Ag nanoplatelets stabilized with cesium bis(2-hydroxyethyl)dithiocarbamate in 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (Uvacure 1500; CAS number: 2386-87-0) f) 41.2 wt-% Ag nanoplatelets stabilized with diethanolammonium dihydroxyethyldithiocarbamate in ethyl-3-ethoxypropionate (763-69-9) g ) 41.2 wt-% Ag nanoplatelets stabilized with diethanolammonium dihydroxyethyldithiocarbamate in 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate (Uvacure 1500, 2386-87-0) 7:f6 t=.) n >
o u, " Lo ,c, 4, .4 r., o r., Y' oD Table lb. Composition of the UV-Vis radiation curable screen printing inks El - E8 Ingredient Commercial name Amount [wt-%] N

El E2 E3 E4 E5 E6 E7 E8 w t.) , I-Polyvinylchloride copolymer Vinnole H14/36 7.4 o 1-, w o Cycloaliphatic epoxide Uvacure 1500 30.1 30.1 30.1 33.6 36.8 36.8 20 31.1 -.., Cationically curable CHDME-di 16.2 16.2 monomer DVE-3 6.1 6.1 6.1 13.7 16.8 16.8 Radically curable oligomer Ebecryl 2959 4.5 4.5 4.5 4.5 Radically curable monomer TMPTA 9.1 9.1 9.1 9.1 Perfluoropolyether Fluorolink E10H
2.5 surfactant Cationic photoinitiator Speedcure 976 5.9 5.9 5.9 5.9 =P
Speedcure 976D 11.5 11.5 11.5 11.5 Free radical photoinitiator Omnirad 2100 3.1 3.1 3.1 3.1 Dispersion DI 31.3 Dispersion 02 31.3 31.3 Dispersion 03 31.3 Dispersion Ag Dispersion 04 nanoplatelets Dispersion 05 25 it r) Dispersion 06 31.3 .t.!
tt Dispersion 07 31.3 It N

Type of ink Hybrid Hybrid Hybrid Cationic Cationic Cationic Hybrid Cationic k.) 1-, e7 Ag nanoplatelets (wt-%) 12.8 12.6 12.6 12.6 10.1 10.2 12.9 12.9 ceo 1-, 1-, Amount of solvent (wt-`)/0) 21.4 21.6 21.6 18.7 0 0 18.4 0 t-) N

Cl. Preparation of security inks (El ¨ E8) and dichroic security features thereof Cl a. Preparation of the security inks El ¨ E8 Ingredients provided in Table lb were independently mixed and dispersed at room temperature using a Dispermat CV-3 for 10 minutes at 2000 rpm so as to yield 50g of the inks El ¨ E8.

Cl b. Preparation of security features The UV-Vis radiation curable screen printing hybrid security inks El ¨ E8 were independently applied on pieces of transparent polymer substrate (PET HostaphanCi RN, thickness 501..Lm, supplied by Putz GmbH + Co. Folien KG) using a 160 thread/cm screen (405 mesh). The printed pattern had a size of 10 5 cm x 5 cm. 10 seconds after the printing step, the pieces of printed substrate were independently cured at room temperature by exposing them two times at a speed of 100 m/min to UV-Vis light under a dryer from 1ST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/cm2 +
mercury lamp 200 W/cm2), to generate security features.
15 C1c. Results (optical properties) of security features The optical properties of each security features obtained at item Cl b were independently assessed in reflection, in transmission, and visually using the three tests described below. The results are summarized in Table lc.
20 Reflection measurements were performed using a goniometer (Goniospektrometer Codec WI-10 5&5 by Phyma GmbH Austria). The Va*b* values of the printed security features were determined at 0 to the normal with an illumination angle of 22.5' on the side of the transparent polymer substrate that was printed. The C* values (chroma, corresponding to a measure of the color intensity or color saturation) were calculated from a* and b* values according to the CIELAB (1976) color space, wherein:
25 C = ce)2 + (if)2 The C* values (reflection 22.5/0 ) are displayed in Table lc below.
Transmission measurements were carried out using a Datacolor 650 spectrophotometer (parameters:
integration sphere, diffuse illumination (pulse xenon D65) and 8' viewing, analyzer SP2000 with dual 30 256 diode array for wavelength range of 360-700nm, transmission sampling aperture size of 22mm).
The C* values (transmission 8 ) are displayed in Table lc below.
A visual assessment was carried out observing each security feature with the naked eye in reflection with a diffuse source (such as the light coming through a window without direct sun, the observer facing 35 the wall opposite to the window). The following colors have been observed:
Dark brown to brown colors with matte appearance and no metallic effect;
Gold color (i.e. metallic yellow color) with glossy appearance and metallic effect. The metallic effect appears for a chroma value C* in reflection 22.5/0' higher than about 20.
A visual assessment was also carried out observing each security feature with the naked eye in 40 transmission. The following colors have been observed:
Dull blue: the blue coloration is weak (but visible);

-Blue (chroma value C* in transmission 8 higher than or equal to about 20) to deep blue (chrorna value C* in transmission 8' higher than or equal to 30): the blue coloration is intense to very intense.
Table lc. Color properties of security features obtained from inks El ¨ E8 El E2 E3 E4 E5 E6 E7 C* (reflection 22.5/0 ) 25 28 28 31 28 27 35 C* (transmission 8 ) 39 41 42 42 44 44 36 Color (reflection) Gold Gold Gold Gold Gold Gold Gold Gold Deep Deep Deep Deep Deep Deep Deep Deep Color (transmission) blue blue blue blue blue blue blue blue As shown in Table lc, the security features obtained from cationically curable or hybrid (cat/rad) inks El ¨ E8 exhibited gold color in reflection and blue to deep blue color in transmission.
Cid. Study of the stability of the UV-Vis radiation curable security ink E7 via an accelerated ageing experiment To evaluate the stability upon time of an ink according to the invention, 10 g of ink E7 (described in Table lb) were placed in a cup (60 ml white polypropylene cup for SpeedMixerTm available at Hauschild & Co. KG), which was hermetically sealed and stored for five months at a temperature of 60 C in a laboratory oven (Kendro Laboratory Products, T6060). The freshly prepared ink E7 was used as a comparison standard. Each month, the sample of ink E7 stored in the oven was cooled at room temperature for 6 hours, and subsequently applied on a piece of transparent polymer substrate (PET Hostaphane RN, thickness 50 m, supplied by Putz GmbH + Co. Folien KG) using a 160 thread/cm screen (405 mesh). The printed pattern had a size of 5 cm x 5 cm. 10 seconds after the printing step, the piece of printed substrate was cured at room temperature by two times exposure at a speed of 100 m/min to UV-Vis light under a dryer from 1ST Metz GmbH (two lamps: iron-doped mercury lamp 200 W/cm2 + mercury lamp 200 W/cm2), to generate a security feature. The optical properties of the security feature obtained each month were independently assessed in reflection, and visually using the tests described at item Clc. Table ld summarizes the color in reflection and transmission and the C* values (reflection 22.5/0 ) exhibited by the security features.
Table id. Color properties of security features Time interval (months) @ 60 C Oa) 1 2 3 4 C* (reflection 22.5/0 ) 35 37 34 35 35 Color (reflection) Gold Gold Gold Gold Gold Gold Deep Deep Deep Deep Deep Deep Color (transmission) blue blue blue blue blue blue a) the security feature was manufactured with the freshly prepared ink E7 according to the present invention.

As attested by the optical properties of security features shown in Table id, the ink E7 remains stable over an extended period of time at high temperature, which is an indication of outstanding shelf stability at room temperature.

Claims

1. A composition, comprising silver nanoplatelets, wherein the silver nanoplatelets are capped by a dithiocarbamate anion of formula , wherein R41 is a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R42 is a Ci-Caalkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups.

2. The cornposition according to claim 1, wherein the composition of the dithiocarbamate capped silver nanoplatelets is prepared i) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets; or ii) by reacting CS2 with an amine of formula R41R42N1-1 in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and a base; or iv) by reacting CS2 with an amine of formula R41R42NH in the presence of a base to obtain a compound of formula , which is then reacted with a composition of silver nanoplatelets; wherein R41 and R42 are defined in claim 1, Catk+ is a cation and k is 1, or 2.

3. The composition according to claim 1, or 2, wherein R41 is a -CH2CH2OH group, a -CH2CH(OH)CH3 group, or a -CH2CH2CH2OH group;
and R42 is a -CH2CH2OH group, a -CH2CH(OH)CH3 group, or a -CH2CH2CH2OH group.

4. The composition according to claim 2, or 3, wherein the base is selected from alkali metal hydroxides, alkali metal alkoxides, amines of formula R43.-,44 R45N and mixtures thereof, wherein R43 is a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R44 is a Cl-C4alkyl group, or a C2-C4alkyl group, which is substituted by one, or two hydroxy groups, and R45 is H, a Ci-C4alkyl group, or a 02-C4alkyl group, which is substituted by one, or two hydroxy groups.

5. The composition according to any of claims 1 to 4, wherein the dithiocarbamate capped silver nanoplatelets are prepared i) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets, ii) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with diethanolamine in the presence of a composition of silver nanoplatelets and a base; wherein the base is selected from alkali metal hydroxides, alkali metal alcoholates and amines of formula R43R44R45N and mixtures thereof, wherein R43 is a C2-C4alkyl group, which is substituted by one hydroxy group, R44 is a C2-C4alkyl group, which is substituted by one hydroxy group, and R45 is H, or a C2-C4alkyl group, which is substituted by one hydroxy group;
iv) by reacting CS2 with diethanolamine in the presence of alkali metal alcoholates, or alkali metal hydroxides to obtain a compound of formula , wherein Cat+ is an alkali metal cation and then reacting the compound of formula (XXIa) with a composition of silver nanoplatelets.

6. The composition according to any of claims 1 to 5, wherein the number mean diameter of the silver nanoplatelets, present in the composition, is in the range of 50 to 150 nm and the number mean thickness of the silver nanoplatelets, present in the composition, is preferably in the range of 5 to 30 nm and the mean aspect ratio of the silver nanoplatelets is preferably higher than 2.0, wherein the number mean diameter and the number mean thickness are determined by transmission electron microscopy.

7. The composition according to claim 6, wherein the highest wavelength absorption maximum of the population of all silver nanoplatelets in the composition being within the range of 560 to 800 nm, especially 600 to 800 measured in water at ca.
5"10-5 M
(mol/l) concentration of silver.

8. The composition according to claim 6, wherein the number mean diameter of the silver nanoplatelets is in the range of 70 to 120 nm with standard deviation being less than 50% and the number mean thickness of the silver nanoplatelets is in the range of 8 to 25 nm with standard deviation being less than 30% and the mean aspect ratio of the silver nanoplatelets is higher than 2.5, wherein the number mean diameter and the number mean thickness are determined by transmission electron microscopy.

9. The composition according to any of claims 1 to 8, wherein the silver nanoplatelets bear at least a surface stabilizing agent which is selected from polymers of formula wherein R1 is H, C1-Ci8alkyl, phenyl, Ci-Csalkylphenyl, or CH2COOH;
R2, R3, R4, R5, R6 and R7 are independently of each other H, Ci-Csalkyl, or phenyl;
Y is 0, or NR8;
R8 is H, or Ci-Csalkyl;
kl is an integer in the range of from 1 to 500, k2 and k3 are independently of each other 0, or integers in the range of from 1 to 250;
k4 is 0, or 1, k5 is an integer in the range of from 1 to 5, and surface stabilizing agents, which are polymers, or copolymers, which are obtained by a process comprising the steps 11) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one nitroxylether having the structural elernent wherein X represents a group having at least one carbon atom and is such that the free radical X. derived from X is capable of initiating polymerization; or i2) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one stable free nitroxyl radical <Evm> and a free radical initiator; wherein at least one monomer used in the steps il) or i2) is a Ci-C6alkyl or hydroxyCi-C6alkyl ester of acrylic or methacrylic acid; and optionally ii) a second step, comprising the modification of the polymer or copolymer prepared under 11) or 12) by a transesterification reaction, an amidation, hydrolysis or anhydride modification or a combination thereof; and mixtures thereof.

10. The composition according to claim 9, wherein the silver nanoplatelets bear at least a surface stabilizing agent which is selected from copolymers represented by formula ' (111), wherein R11 and R12 are H or methyl, R13, Ra and FL, are independently of each other H or methyl, Rb is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, Ru iS RA-[0-CH2-CH2-]nl-0-5 R14 is -C(=0)-N-(CH2)yNR15R165 or -C(=0)-N-(CH2)yNHR15R16+An-5 wherein An- is an anion of a monovalent organic, or inorganic acid;
y is an integer from 2 to 10;
R15 is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, R1 is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, RA is saturated or unsaturated, linear or branched chain alkyl with 1-22 carbon atoms, or alkylaryl or dialkylaryl with up to 24 carbon atoms;
n1 is 1 to 150, m, n and p are independently of each other integers from 1 to 200, and o is an integer from 1 to 150; and polymers of formula wherein R1 is H, or a Cl-Csalkyl group, and kl is 22 to 450, especially 22 to 150 and mixtures thereof.

11. The composition according to any of claims 1 to 10, which comprises one, or more stabilizing agents selected from the group consisting of compounds of formula wherein R2la is a hydrogen atom, a halogen atom, a 01-C8alkoxy group, or a C1-C8alkyl group, R2lb is a hydrogen atom, or a group of formula -CHR24-N(R22)(R23), R22 and R23 are independently of each other a Ci-Csalkyl, a hydroxyCi-Csalkyl group, or a group of formula -RCH2CH2)-01n2-CH2CH2-0H, wherein n2 is 1 to 5, R24 is H or Ci-Csalkyl, and compounds of formula wherein R25 can be the same, or different in each occurrence and is a hydrogen atom, a halogen atom, a Ci-Cisalkyl group, a Ci-Cisalkoxy group, or a group -C(=0)-R26, R26 is a hydrogen atom, a hydroxy group, a Ci-Cisalkyl group, unsubstituted or substituted aminogroup, unsubstituted or substituted phenyl group, or a Ci-Cisalkoxy group, and n3 is a number of 1 to 4, m3 is a number of 2 to 4, and the sum of m3 and n3 is 6.

12. The composition according to any of claims 1 to 11, which comprises at least one surface stabilizing agent selected from the group consisting of MPEG
2000 thiol (A-1, average Mr, 2,000), MPEG 3000 thiol (A-2), MPEG 4000 thiol (A-3) MPEG 5000 thiol (A-4), MPEG 6000 thiol (A-5), PEG thiols (0-(2-mercaptoethyl)-poly(ethylene glycol)) having an average Mn of 2000 to 6000, such as, for example, PEG 2000 thiol (A-6, average Mn 2,000), PEG 3000 thiol (A-7), PEG 4000 thiol (A-8), PEG 5000 thiol (A-9), PEG 6000 thiol (A-1 0);
at least one surface stabilizing agent selected from copolymers represented by formula (111), where R11 and R12 are H or methyl, m, n and p are independently of each other integers from 1 to 200, o is an integer from 1 to 150, especially an integer from 1 to 149; and at least one stabilizing agent selected from the group consisting of compounds of

13. A process for producing the composition according to any of claims 1 to 12, comprising i) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets; or ii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and subsequent treatment with a base; or iii) by reacting CS2 with an amine of formula R41R42NH in the presence of a composition of silver nanoplatelets and a base; or iv) by reacting CS2 with an amine of formula R41R42NH in the presence of a base to obtain a compound of formula which is then reacted with a composition of silver nanoplatelets; wherein R41 and R42 are defined in claim 1, Catk+ is a cation and k is 1, or 2.

14. The process according to claim 13, wherein the composition of the silver nanoplatelets, is prepared by a process, which comprises:
(a) preparing a solution (a) comprising a silver precursor, a compound of formula wherein R1 is H, Ci-Cisalkyl, phenyl, Ci-Csalkylphenyl, or CH2COOH;
R2, R3, ri R5, R6 and R7 are independently of each other H, Cl-Csalkyl, or phenyl;
Y is 0, or NR8;
R8 is H, or Ci-C8alkyl;
kl is an integer in the range of from 1 to 500, k2 and k3 are independently of each other 0, or integers in the range of from 1 to 250;
k4 is 0, or 1, k5 is an integer in the range of from 1 to 5;

and a polymer, or copolymer which can be obtained by a process comprising the steps 11) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one nitroxylether having the structural element wherein X represents a group having at least one carbon atom and is such that the free radical X. derived from X is capable of initiating polymerization; or i2) polymerizing in a first step one or more ethylenically unsaturated monomers in the presence of at least one stable free nitroxyl radical and a free radical initiator; wherein at least one monomer used in the steps i1) or i2) is a Ci-C6 alkyl or hydroxy Ci-Csalkyl ester of acrylic or methacrylic acid; and optionally ii) a second step, comprising the modification of the polymer or copolymer prepared under il) or i2) by a transesterification reaction, an amidation, hydrolysis or anhydride modification or a combination thereof;
water, and optionally a defoamer;
(b1) preparing a solution (b), comprising a reducing agent, which comprises at least one boron atom in the molecule, and water;
(b2) adding solution (a) to solution (b), and adding one or more complexing agents;
(c) adding a hydrogen peroxide solution in water; and (d) optionally adding a stabilization agent to the mixture obtained in step (c), thereby synthesizing the composition, comprising the silver nanoplatelets.

15. A composition, comprising silver nanoplatelets, which is obtained by the process according to claim 13, or 14.