MICROPARTICLE COMPOSITION COMPRISING AN IR-ABSORBING ORGANIC PIGMENT

Abstract

The present invention relates to microparticle compositions comprising an IR-absorbing organic pigment having a principal absorption maximum in the 750 to 1100 nm range. The invention also relates to a process for producing such microparticle compositions and their use in a printing ink, particularly a printing ink suitable for producing a security feature or security document. The microparticles of the pigment composition contain the IR-absorbing organic pigment as solid particles, surrounded or embedded in an aminoplastic polymer, which is a polycondensation product of one or more amino compounds and one or more aldehydes. The microparticle-based pigment composition is characterized by a volume-based particle size distribution, determined by static light scattering according to ISO 13320:2009 EN, having a D(4) value.3) in the range of 1.0 to 15.0 µm.

Description

The present invention relates to microparticle compositions comprising an infrared (IR) absorbing organic pigment having a principal absorption maximum in the 750 to 1100 nm range. The invention also relates to a process for producing such microparticle compositions and their use in a printing ink, particularly a printing ink suitable for producing a security feature or security document. BACKGROUND OF THE INVENTION Colorless or barely colored IR absorbers meet an important technical need in a wide range of applications, such as security printing (banknotes, credit cards, ID cards, passports, etc.), invisible and / or IR-readable barcodes, laser welding of plastics, curing of surface coatings with IR radiators, drying and curing of prints, fixing toners on paper or plastics, optical filters for PDPs (plasma display panels), laser marking, for example, of paper or plastics, heating of plastic preforms, or thermal shielding applications. A large number of organic and inorganic substances belonging to different compound classes and with a wide variety of structures are known for use as IR absorbers (see, for example, EP30672216 and the reference cited therein). Despite the large number of known compound classes and structures, providing products with a complex property profile often presents challenges. There is a continuous demand for IR absorbers that are “colorless,” meaning they have the least possible inherent color and simultaneously meet technical stability requirements, such as chemical stability, heat stability, and light stability. Unfortunately, the chemical stability of IR-absorbing pigments is often unsatisfactory. In particular, IR-absorbing pigments with a principal absorption maximum in the 750–1100 nm range and that are colorless can be unstable, especially under oxidative stress. Consequently, there is still a need for high-level applications of IR-absorbing compounds to improve their oxidation-fastness properties. This property is particularly important for security printing applications. It is of paramount importance in security printing applications that the IR absorption properties remain high after the drying / hardening stage of the printing ink and that the IR spectrum remains essentially unchanged compared to its initial state before the drying / hardening stage.It is also essential that the security feature of the printing ink does not undergo any significant change in its absorption characteristics during the lifespan of the security document. Finally, it is essential that the infrared-absorbing pigment contained in the printing ink does not degrade before the ink is actually used (shelf-life stability). WO 2017 / 080652 describes safety pigments in the form of core-coat particles, which have a core made of a thermoplastic polymer containing a UV, VIS, or IR dye and a coating formed by a condensation polymer such as a melamine formaldehyde resin. The preparation includes the preparation of colorant-containing polymer particles, followed by incorporating the resulting polymer particles into a thermoplastic matrix, grinding the resulting matrix, and encapsulating the resulting colorant-containing polymer particles with the condensation polymer. The resulting core-coat particles contain only small amounts of the dye. Furthermore, this concept is applicable only to colorants that are soluble in organic solvents and compatible with the thermoplastic polymer. WO 2017 / 080656 describes safety pigments in the form of core-coat particles, which have a core made of a crosslinked thermoset polymer containing a UV, VIS, or IR dye and a coat formed by an addition polymer such as a melamine formaldehyde resin. The preparation of these pigments is tedious. It requires the preparation of dye-containing polymer particles, followed by the incorporation of the dye into a thermoset matrix, the grinding of the resulting matrix, and the encapsulation of the resulting dye-containing polymer particles by condensation polymer. The resulting core particles must contain only small amounts of dye. Furthermore, this concept is only applicable to dyes that can be incorporated into the thermoset polymer matrix. EP30672216 describes pigment compositions containing an IR absorbent and a stabilizing agent selected from thioamide, thiourea, and thiocarbamate compounds, such as thiocyanuric acid, diphenylthiourea, dibutylthiourea, diisopropylthiourea, 2-mercapto-1-methylimidazole, 2-mercaptobenzimidazole, and N-phenylthioacetamide, and their tautomers such as 2-thiomercaptopyrimidine compounds. While these compositions provide improved stability to IR-absorbing pigments against both chemicals and light and do not impart color, the low molecular weight stabilizing compounds may not always be acceptable, and long-term stability may not always be satisfactory, as the stabilizers may degrade on their own. Therefore, there is a need for IR-absorbing organic pigment compositions that can be easily prepared from conventional IR-absorbing pigments, particularly organic IR-absorbing pigments that provide improved stability, especially against the oxidative stress that occurs in oxidatively drying printing inks. Furthermore, the pigment composition must be compatible with printing inks and easily incorporated into them, particularly oxidatively drying printing inks. BRIEF DESCRIPTION OF THE INVENTION Surprisingly, microparticle-based pigment compositions of an IR-absorbing organic pigment as described herein were found to meet the requirements for technical stability, particularly chemical stability, and can be readily incorporated into printing inks. Therefore, the present invention relates to pigment compositions based on microparticles of an IR-absorbing organic pigment having a principal absorption maximum in the range of 750 to 1100 nm, wherein the microparticles of the pigment composition contain the IR-absorbing organic pigment as solid particles, which are surrounded or embedded in an aminoplastic polymer, which is a polycondensation product of one or more amino compounds and one or more aldehydes, wherein the microparticle-based pigment compositions are characterized by a volume-based particle size distribution, determined by static light scattering according to ISO 13320:2009 EN, having a D(4.3) value in the range of 1.0 to 15.0 pm, particularly in the range of 3.0 to 12.0 pm. The present invention also relates to a method for producing the microparticle-based pigment composition of the invention, comprising the following steps: i) providing an aqueous suspension of the IR-absorbing solid organic pigment that also contains an aminoplastic precondensate of one or more amino compounds and one or more aldehydes; ii) perform the polycondensation of the aminoplastic precondensate in the aqueous suspension of the IR-absorbing solid organic pigment in the presence of at least one surfactant. The invention also relates to the use of the microparticle-based pigment composition of the invention in a printing ink, in particular in an oxidative drying printing ink, specifically a printing ink suitable for intaglio printing. Another aspect of the invention relates to a printing ink, in particular a security printing ink containing a microparticle-based composition as described herein and a binder, in particular an oxidative drying binder. Another aspect of the invention relates to a method for producing a security feature or security document, comprising applying the printing ink of the invention to a substrate by a printing process. The present invention is associated with several advantages. The microparticle-based compositions of the invention provide enhanced stability to the IR-absorbing pigments contained therein, particularly stability to chemicals and light. In particular, the compositions provide enhanced stability to oxidative stress, as occurs in oxidatively curing printing inks. Therefore, the IR absorption properties remain high after the drying / hardening stage of the printing ink, and the IR spectrum remains essentially unchanged compared to its initial state before the drying / hardening stage. Furthermore, the compositions of the invention have good long-term stability and do not require the use of additional stabilizers. Moreover, the compositions can be easily incorporated into printing inks.The process of the invention allows for the incorporation of high quantities of the IR-absorbing organic pigment into the composition. Therefore, it is possible to obtain compositions containing high quantities of the IR-absorbing organic pigment and comparatively low quantities of other ingredients, which could affect the pigment's IR absorbance or other properties. In contrast, the microparticle-based compositions of the invention have an IR absorption profile that is essentially unaffected by their protective aminoplastic coating, compared to the original, untreated organic pigment. DETAILED DESCRIPTION OF THE INVENTION In this document and throughout the specification, the expression “microparticle-based composition” refers to discrete microparticle compositions. The term “microparticle” indicates that the discrete particles typically have a particle size not exceeding a few micrometers or even smaller, for example, in the nanometer range. In particular, the term “microparticle” indicates that at least 90% by volume of the particles, based on the total volume of particles contained in the composition, have a particle size of less than 25 pm, particularly 20.0 pm at most, more particularly 17.5 pm at most, and especially 15.0 pm at most, given as the value D(v 0.9). Particle size, as referred to herein, and particle size distribution, characterized, for example, by the values ​​D(v 0.1), D(v 0.5), D(v 0.9), D(3.2), and D(4.3), is the diameter of the particles, for example, pigment particles as well as pigment-polymer particles, which can be determined by techniques such as laser diffraction, also called static light scattering (SLS). SLS is generally performed in accordance with ISO 13320:2009 EN. In the context of particle size, the particle size value D(0.9) or D(v 0.9) indicates that 90% of the particles by volume have a hydrodynamic diameter less than this value. Similarly, the volumetric mean particle diameter value D(0.5) or D(v 0.5) means that 50% of the particles by volume have a diameter greater than this value, and 50% have a diameter less than this value. Furthermore, the particle size value D(0.1) or D(v 0.1) indicates that 10% of the particles by volume have a hydrodynamic diameter less than this value. D(3.2) describes the surface-weighted average diameter of all particles, while D(4.3) describes the volume-weighted average diameter of all particles. The microparticles contained in the microparticle-based composition include an IR-absorbing organic pigment and an aminoplastic polymer. The IR-absorbing organic pigment is embedded in or surrounded by the aminoplastic resin. The aminoplastic polymer contained in the microparticle composition of the present invention is a polycondensation product of one or more amino compounds and one or more aldehydes. The amino compounds useful in this respect are amines that have at least two amino groups, particularly two or three. These amines are preferably characterized by the fact that each of their amino groups is attached to a carbon atom that is double-bonded to an oxygen, sulfur, or nitrogen atom. Preferred examples of such amines are urea, thiourea, melamine, cyanoguanamine (dicyandiamide), acetoguanamine, and benzoguanamine. The aldehydes useful in this respect are the C1-C10 alkanes, especially the C1-C4 alkanes, such as formaldehyde, acetaldehyde, propanal, or n-butanal, and the C2-C10 alkanedials, especially the C2-C6 alkanedials, such as glyoxal or glutaraldehyde. The preferred aldehydes are formaldehyde, glyoxal, and glutaraldehyde, particularly formaldehyde. The aminoplastic polymer may be partially or fully etherified. The aminoplastic polymer of the microparticle composition of the invention is typically selected from melamine-formaldehyde resins (= MF resins), including wholly or partially etherified MF resins, urea-formaldehyde resins (= UF resins), thiourea-formaldehyde resins (= TUF resins), melamine-urea-formaldehyde resins (= MUF resins), including wholly or partially etherified MUF resins, melamine-thiourea-formaldehyde resins (= MTUF resins), including partially etherified MTUF resins, ureaglutaraldehyde resins, benzoguanamine-formaldehyde resins, dicyandiamide-formaldehyde resins, and urea-glyoxal resins, i.e., from polymers obtained by polycondensation of melamine, urea, thiourea, mixtures of melamine / (thio)urea, benzoguanamine or dicyandiamide with formaldehyde, by polycondensation of urea with glutaraldehyde, or by polycondensation of urea with glyoxal. The aminoplastic polymer of the microparticle composition of the invention is preferably selected from MF resins, including totally or partially etherified MF resins and melamine-urea-formaldehyde resins (= MUF resins), including totally or partially etherified MUF resins, in particular is an MF resin, and especially totally or partially etherified MF resins. The amount of aminoplastic polymer in the microparticle composition of the present invention is typically 15 to 50% by weight, particularly 17 to 45% by weight, and especially 19 to 42% by weight, based on the total weight of the aminoplastic polymer and the IR-absorbing organic pigment. Accordingly, the amount of IR-absorbing pigment in the microparticle composition of the present invention is typically 50 to 85% by weight, particularly 55 to 83% by weight, and especially 68 to 81% by weight, based on the total weight of the aminoplastic polymer and the IR-absorbing organic pigment. In principle, any known IR-absorbing organic compound having a principal absorption maximum in the 750–1100 nm range is suitable for use as the IR-absorbing organic pigment contained in the microparticle-based composition of the invention. Preference is given to IR-absorbing pigments that are “colorless,” meaning they have minimal absorption in the visible (VIS) range of the electromagnetic spectrum, particularly in the 400–700 nm range. The pigments according to the present invention are polyunsaturated polycyclic organic compounds or metal-organic compounds, having a principal absorption maximum in the range of 750 to 1100 nm. Particular preference is given to polycyclic organic metal-organic compounds, in particular to complexes of mono- or polyunsaturated mono- or polyunsaturated organic compounds with a metal or semimetal, wherein the mono- or polyunsaturated mono- or polycyclic organic compound together with the metal or semimetal atom forms a polyunsaturated polycyclic organic metal-organic compound. The pigments of the present invention consist primarily of polyunsaturated polycyclic organic compounds or metal-organic compounds.The organic pigments according to the present invention contain in particular less than 60% by weight, in particular less than 50% by weight or less than 40% by weight, or even less than 30% by weight, based on the total weight of the pigment, of organic matter that does not have a principal absorption maximum in the range of 750 to 1100 nm. Frequently, the IR-absorbing organic pigment is selected from the group consisting of metal dithiolene complexes, phthalocyanine pigments, naphthalocyanine pigments, rylene pigments, polymethine pigments, and anthraquinone pigments, in particular those described in detail in EP 3 067 216, which is incorporated herein by reference, as well as mixtures of these pigments. More preferably, the IR-absorbing organic pigment of the microparticle composition of the invention is selected from naphthalocyanine pigments and metal dithiolene complexes. Suitable naphthalocyanine pigments are those of formulas l11, l112, and l113 described in EP 3067216, which is incorporated herein by reference. Suitable metal dithiolene complexes are those described, for example, by formulas H1a and l11b in EP 3067216 and in particular those described by formula (I) of WO 2008 / 086931 or by formula (I) of WO 2012 / 069518, which are incorporated herein by reference. In a particular embodiment of the present invention, the IR-absorbing organic pigment of the microparticle composition of the invention is selected from the group consisting of metal dithiolene complexes of formula (I), wherein M is Ni, Pd or Pt, X1, X2, independently of each other, are O or S, R1, R2, R3 and R4 are the same or different and are selected from the group consisting of alkyl, where one or more non-adjacent alkyl radicals can be replaced by o, alkenyl, aryl and hetaryl, where aryl and hetaryl are either unsubstituted or substituted. Here and throughout the descriptive memory, the term “alkyl” refers to a linear or branched saturated hydrocarbon radical normally having 1 to 18 carbon atoms, in particular 1 to 12 carbon atoms, frequently 1 to 6 carbon atoms, in particular 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, π-hexyl, 2-hexyl, 2,3-dimethylbutyl, n-heptyl, 2-heptyl, noctyl, 2-octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, n-nonyl, 2-nonyl, n-decyl, 2-decyl, n-undecyl, 2undecyl, n-dodecyl, 2-dodecyl and 2,4,4,6,6-pentamethyldecyl. Here and throughout the descriptive memory, the term “alkyl, where 1 or more non-adjacent CH2 radicals are replaced by O” refers to a saturated aliphatic radical, linear or branched, usually having 3 to 18 carbon atoms, in particular 4 to 12 carbon atoms, where at least 1 of the CH2 groups, for example, 1, 2, 3 or 4 non-adjacent CH2 groups are replaced by O, thus forming an oxyalkylene group such as methoxymethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-propoxyethyl, 2-methoxypropyl, 2-ethoxypropyl, 3-methoxypropyl, 3-ethoxypropyl, 2-(2-methoxyethoxy)ethyl, 2-(2-ethoxyethoxy)ethyl, 2-(2-methoxyethoxy)propyl, 2-(2-ethoxyethoxy)-propyl, 2-(2-methoxypropoxy)-propyl, 2-(2-ethoxypropoxy)-propyl, 3-(2-methoxyethoxy)-propyl, 3-(2-ethoxyethoxy)-propyl, 2-(2-(2-methoxyethoxy)ethoxyjetyl, 2-(2-(2-ethoxyethoxy)-ethoxy)ethyl, 2-(2-(2-methoxyethoxy)-ethoxy¡)propyl, 2-(2-(2-ethoxyethoxy)-ethoxy¡)propyl, 3-(2-(2-methoxyethoxy)-ethoxy¡)propyl, 3-(2-(2-ethoxyethoxy)-ethoxy¡)propyl, etc.Here and throughout the descriptive memory, the term “alkenyl” refers to a linear or branched unsaturated hydrocarbon radical usually having 2 to 18 carbon atoms, in particular 3 to 12 carbon atoms, frequently 3 to 6 carbon atoms, and bearing at least one ethylenically unsaturated double bond, such as ethenyl, 1-propenyl, 2-propenyl, 1-methylethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-methyl-1-propenyl, 2-methyl-1-propenyl, 1-methyl-2-propenyl, or 2-methyl-2-propenyl; C2-C6 alkenyl, such as ethenyl, 1-propenyl, 2-propenyl, 1-methylethenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1-methyl-1-propenyl, 2-methyl-1-propenyl, 1-methyl-2-propenyl, 2-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-methyl-1-butenyl, 2-methyl-1-butenyl, 3-methyl-1-butenyl, 1methyl-2-butenyl, 2-methyl-2-butenyl, 3-methyl-2-butenyl, 1-methyl-3-butenyl, 2-methyl-3-butenyl, 3-methyl-3-butenyl, 1,1-dimethyl-2-propenyl, 1,2-dimethyl-1-propenyl, 1,2-dimethyl-2-propenilo, 1-etil-1-propenilo, 1 -etil-2propenilo, 1-hexenilo, 2-hexenilo, 3-hexenilo, 4-hexenilo, 5-hexenilo, 1-metil-1-pentenilo, 2-metil-1pentenilo, 3-metil-1-pentenilo, 4-metil-1-pentenilo, 1-methyl-2-pentenilo, 2-methyl-2-pentenilo, 3-methyl-2pentenilo, 4-methyl-2-pentenilo, 1-methyl-3-pentenilo, 2-methyl-3-pentenilo, 3-methyl-3-pentenilo, 4-methyl-3pentenilo, 1-met¡l-4-penten¡lo, 2-metil-4-pentenilo, 3-metil-4-pentenilo, 4-metil-4-pentenilo, 1, 1-dimetil-2butenilo, 1,1-dimetil-3-butenilo, 1,2-d¡met¡l-1 -butenilo, 1,2-dimetil-2-buten¡lo, 1,2-dimetil-3-buten¡lo, 1,3dimetil-1 -butenilo, 1,3-dimetil-2-buten¡lo, 1,3-dimetil-3-buten¡lo, 2,2-dimetil-3-butenilo, 2,3-d¡met¡l-1 butenilo, 2,3-dimetil-2-butenilo, 2,3-dimetil-3-butenilo, 3,3-d¡met¡l-1 -butenilo, 3,3-dimetil-2-buten¡lo, 1 -etil-1 butenilo, 1 -etil-2-butenilo, 1 -etil-3-butenilo, 2-etil-1-butenilo, 2-etil-2-butenilo, 2-etil-3-butenilo, 1,1,2trimetil-2-propenilo, 1-etil-1-metil-2-propenilo, 1-etil-2-metil-1 -propenilo,1-ethyl-2-methyl-2-propenyl, and the like, or C2-C8 alkenyl, such as the radicals mentioned for C2-C8 alkenyl, and additionally 1-heptenyl, 2-heptenyl, 3-heptenyl, 1-octenyl, 2-octenyl, 3-octenyl, 4-octenyl and their positional isomers. Here and throughout the descriptive memorandum, the term “aryl” refers to mono- and polycyclic aryl, while the term “hetaryl” refers to mono- and polycyclic hetaryl, where the expressions “monocyclic aryl”, “polycyclic aryl”, “monocyclic hetaryl”, and “polycyclic aryl” are as defined herein. Here and throughout this descriptive memorandum, the term “substituted” in the context of aryl and hetaryl means that aryl and hetaryl carry at least one radical other than hydrogen. In particular, the term “substituted” means that aryl and hetaryl are substituted with 1, 2, 3, 4, or 5 Ra radicals as defined below. Here and throughout the descriptive memory, the expressions “monocyclic aromatic radical” and “monocyclic aryl” refer to phenyl. Here and throughout the descriptive report, the term “polycyclic aryl” refers to: (i) a polycyclic aromatic hydrocarbon radical, i.e. a fully unsaturated polycyclic hydrocarbon radical, wherein each of the carbon atoms is part of a conjugated π-electron system, (ii) a polycyclic hydrocarbon radical bearing a phenyl ring fused to a saturated or unsaturated 4- to 10-membered mono- or bicyclic hydrocarbon ring, (iii) a polycyclic hydrocarbon radical bearing at least two phenyl rings fused directly to each other and / or fused to a saturated or unsaturated 4- to 10-membered mono- or bicyclic hydrocarbon ring. Usually, the polycyclic aryl has from 9 to 26, for example, 9, 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, 24, 25 or 26 carbon atoms, in particular from 10 to 20 carbon atoms, especially 10, 12, 13, 14 or 16 carbon atoms. In this context, a polycyclic aryl group bearing 2, 3, or 4 phenyl rings that are directly fused together includes, for example, naphthyl, anthracenyl, phenanthrenyl, pyrenyl, and triphenylenyl. A polycyclic aryl group bearing 2, 3, or 4 phenyl rings fused to a saturated or unsaturated mono- or bicyclic hydrocarbon ring of 4 to 10 members includes, for example, 9H-fluorenyl, biphenylenyl, tetraphenylenyl, acenaphtheniyl (1,2-dihydroacenaphtheniyl), acenaphtheniyl, 9,10-dihydroanthracen-1-yl, 1,2,3,4-tetrahydrophenanthrenyl, 5,6,7,8-tetrahydrophenanthrenyl, cyclopent[fg]acenaphtheniyl, phenalenyl, fluorantheniyl, benzo[k]fluorantheniyl, perilenyl, 9,10-dihydro-9,10[1',2']-benzenoanthracenyl, dibenzo[a,e][8]anulenyl, 9,9'spirobi[9 / 7-fluoren]¡lo and spiro[1 / 7-cyclobuta[ote]naphthalene-1,9'-[9 / - / ]fluoren]¡lo. The arilo polycyclic include, by way of example, naftilo, 9H-fluorenilo, fenantrilo, antracenilo, pyrenilo, acenaftenilo, acenaftilenilo, 2,3-dihidro-1H-indenilo, 5,6,7,8-tetrahydro-naphthalenilo, ciclopent[fg]acenaftenilo, 2,3-d¡hidrofenalenilo, 9,10-dihidroantracen-1-ilo, 1,2,3,4-tetrahydrofenantrenilo, 5,6,7,8-tetrahydrofenantrenilo, fluorantenilo, benzo[k]fluorantenilo, biphenylenilo, triphenylenilo, tetraphenylenilo, 1,2-dihidroacenaftenilo, dibenzo[a,e][8]annulenilo, perilenilo, bifenililo, terfenililo, naphthilenfenilo, fenantrilfenilo, antracenilfenilo, pyrenilfenilo, 9H-fluorenilfenilo, di(naphthilen)fen¡lo, naphthilenbifenilo, tri(phenyl)fen¡lo, tetra(phenyl)fenilo, pentaphenyl(phenyl), fenilnaftilo, binaftilo, fenantrilnaftilo, pyrenilnaftilo, fenilantracenilo, bifenilantracenilo, naphthalenylantracenilo, fenantrilantracenilo, dibenzo[a,e][8]anulenilo, 9,10-dihidro-9,10[r,2']benzoantracen¡lo, 9,9'-espirobi-9H-fluoren¡lo and espiro[1 / 7-cyclobuta[c / e]naphthalen-1,9'[9H]fluoren]ilo. Here and throughout the descriptive memory, the expressions “monocyclic heteroaromatic radical” and “monocyclic heteroyl” refer to a heteroaromatic monocyclic radical, where the ring member atoms are part of a conjugated π electron system, where the heteroaromatic monocycle has 5 or 6 atoms in the ring, comprising as heterocyclic ring members 1, 2, 3 or 4 nitrogen atoms or 1 oxygen atom and 0, 1, 2 or 3 nitrogen atoms, or 1 sulfur atom and 0, 1, 2 or 3 nitrogen atoms, where the remainder of the ring atoms are carbon atoms. Examples include furyl (= furanyl), pyrrolyl (= 1 H-pyrrolyl), thienyl (= thiophenyl), imidazolyl (= 1Himidazolyl), pyrazolyl (= 1 H-pyrazolyl), 1,2,3-triazolyl, 1,2,4-triazolyl, tetrazolyl, oxazolyl, thiazolyl, isoxazolyl, isothiazolyl, 1,3,4-oxadiazolyl, 1,3,4-thiadiazolyl, pyridyl (= pyridinyl), pyrazinyl, pyridazinyl, pyrimidinyl and triazinyl. Herein and throughout the descriptive memorandum, the term “polycyclic hetaryl” refers to a heteroaromatic polycyclic radical, bearing a monocyclic hetaryl ring as defined above and at least one, for example, 1, 2, 3, 4 or 5 additional aromatic rings selected from phenyl and heteroaromatic monocycles as defined above, wherein the polycyclic hetaryl aromatic rings are linked together by a covalent bond and / or fused directly to each other and / or fused to a saturated or unsaturated 4- to 10-membered mono- or bicyclic hydrocarbon ring.The expression “polycyclic hetaryl” also refers to polycyclic heteroaromatic radicals, which have at least one saturated or partially unsaturated 5- or 6-membered heterocyclic ring having 1 or 2 heteroatoms selected from oxygen, sulfur, and nitrogen as ring atoms, such as 2H-pyran, 4H-pyran, thiopyran, 1,4-dihydropyridine, 4H-1,4-oxazine, 4H-1,4-thiazine, or 1,4-dioxin, and at least one, for example, 1, 2, 3, 4, or 5, additional aromatic rings selected from phenyl and heteroaromatic monocycles, wherein at least one of the additional aromatic rings is directly fused to the saturated or partially unsaturated 5- or 6-membered heterocyclic radical and wherein the remaining additional polycyclic hetaryl aromatic rings are linked to each other by a covalent bond or fused together. directly with each other and / or fused to a saturated or unsaturated mono- or bicyclic hydrocarbon ring of 4 to 10 members.Typically, the polycyclic hetaryl has 9 to 26 atoms in the ring, in particular 9 to 20 atoms in the ring, comprising 1, 2, 3 or 4 atoms selected from nitrogen atoms, sulfur atoms and oxygen atoms, where the remainder of the ring atoms are carbon atoms. Examples of polycyclic hetaryl include, but are not limited to, benzofuryl, benzothenyl, dibenzofuranyl (= dibenzo[b,d]furanyl), dibenzothenyl (= dibenzo[b,d]thien¡lo), naphthofuryl, naphthothenyl, furo[3,2-b]furanyl, furo[2,3,3] furo[3,4-b]furanyl, thieno[3,2-b]thienol, thieno[2,3-b]thienol, thienol[3,4b]thienyl, oxanthrenyl, thianthrenyl, indolyl (= 1 H-indolyl), isoindolyl (= 2H-isolinyl), carbalisyl, indolyl benzopyrazolyl, benzimidazolyl, benzoxazolyl, benzothiazolyl, benzo[cd]indolyl, 1Hbenzo[g]indolyl, quinolynyl, isoquinolynyl, acridinyl, phenazinyl, quinazolinyl, quinoxalinyl, phenoxazinyl, phenthiazinyl, phthizolinyl,

[15] cinnalinyl, 1,5-naphthyridinyl, 1,8-naphthyridinyl, phenylpyrrolyl, naphthylpyrrolyl, dipyridyl, phenylpyridyl, naphthylpyridyl, pyrido[4,3-b]indolyl, pyrido[3,2-b]indolyl, pyrido[3,2-quinolyl,] pyrido[2,3-b][1,8]naphthyridinyl, pyrrole[3,2-b]pyridinyl, pteridinyl, puryl, 9H-xantenyl, 9H-thioxanthenyl,2Hcromenyl, 2H-thiocromenyl, phenanthridinyl, phenanthrolinyl, furo[3,2-f ][1]benzofuranyl, furo[2,3f ][1]benzofuranyl, furo[3,2-g]quinolinyl, furo[2,3-g]quinolinyl, furo[2,3-g]quinoxalinyl, benzo[g]chromenyl, thieno[3,2-f ][1 ]benzothienyl, thieno[2,3-f ][1 ]benzothienyl, thieno[3,2-g]qui noli ni lo, thieno[2,3-g]qui nol ini lo, thieno[2,3-g]quinoxalínyl, benzo[g]thiochromenyl, pyrrolo[3,2,1-hi]indolyl, benzo[g]quinoxalin¡lo, benzo[f]quinoxalin¡nílo and benzo[h]isoquinol¡nílo., Here and throughout the descriptive memory, the term “cycloalkyl” refers to a saturated mono- or polycyclic hydrocarbon radical that usually has 3 to 12 carbon atoms, frequently 3 to 8 carbon atoms, in particular 5 to 6 carbon atoms, such as cyclopentyl, cyclohexyl, norbornyl, or adamantyl. The metal atom M in the dithiolene complex of formula (I) is preferably nickel or platinum and in particular it is nickel. The variables X1 and X2 in formula (I) may be different, but preferably they are identical and are both sulfur and oxygen. In a particular preferred embodiment, X1 and X2 are both sulfur. Preferably, the radicals R1, R2, R3 and R4, independently of each other, are selected from Ci-Cs alkyl, phenyl, polycyclic aryl, such in particular naphthyl, mono- and polycyclic hetharyl, such in particular pyridyl, furyl, thienyl, imidazoyl or pyrazolyl, wherein phenyl, polycyclic aryl, mono- and polycyclic hetharyl may be unsubstituted or may be substituted with 1, 2, 3, 4 or 5 Ra radicals. The Ra radicals, independently of each other, are usually selected from the group consisting of halogen, Ci-Cs alkyl, Ci-Cs haloalkyl, Ci-Cs alkoxy, Ci-Cs alkylthio, Cs-Cs cycloalkyl, heterocycloalkyl, aryl, hetaryl, hydroxyl, mercapto, cyano, nitro, COOH, SO3H, and NE1E2, where E1 and E2 are each, independently, hydrogen, Ci-β alkyl, Cs-Cs cycloalkyl, heterocycloalkyl, aryl, or hetaryl. In particular, the Ra radicals, independently of each other, are selected from the group consisting of fluorine, chlorine, bromine, cyano, nitro, C1-C4 alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, or tert.-butyl, C1-C4 haloalkyl, such as fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, dichloromethyl, 2-fluoroethyl, 2,2-difluoroethyl or 2,2,2-trifluoroethyl, C1-C3 alkoxy, such as methoxy, ethoxy, n-propoxy or isopropoxy, Cs-Ce cycloalkyl, such as cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl, aryl, such as phenyl or naphthyl and hetharyl, such as pyridyl, furyl, pyrrolyl, imidazolyl, pyrazolyl or thienyl, in particular selected from fluorine, chlorine, cyano, nitro, methyl, ethyl, n-propyl, isopropyl, fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, 2,2,2-trifluoroethyl, methoxy, ethoxy, phenyl, pyridyl, furyl and thienyl, more particularly selected from methyl, ethyl, isopropyl, fluorine, cyano, nitro, trifluoromethyl, 2,2,2-trifluoroethyl, methoxy and phenyl and specifically from methyl, ethyl, isopropyl, fluorine and trifluoromethyl. In particular, the radicals R1, R2, R3 and R4, independently of each other, are Ci-Cs alkyl or aryl, where aryl is substituted with one or two Ra radicals, having the meanings defined herein, particularly the preferred ones, or is unsubstituted, i.e., does not bear Ra radicals. In the event that the radicals R1, R2, R3 and / or R4 are substituted with two Ra radicals, these two Ra radicals are preferably the same. The radicals R1, R2, R3y R4de particularly prefer to be selected, independently of each other, from methyl, ethyl, π-propyl, isopropyl, π-butyl, 2-butyl, ¡sobutyl, π-hexilo, n-octyl, 2-ethylhexan-1yl, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-ethylphenyl, 3-ethylphenyl, 4-ethylphenyl, 2-isopropylphenyl, 3isopropylphenyl, 4-isopropylphenyl, 3,5-dimethylphenyl, 3,5-diethylphenyl, 3,5-diisopropylphenyl, 2,6-dimethylphenyl, 2,6-Diethylphenyl, 2,6-Diisopropylphenyl, 2-fluorophenyl, 3-fluorophenyl, 4-fluorophenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, pentafluorophenyl, 3,5-difluorophenyl, 2,6-difluorophenyl, 2-difluoromethylphenyl, 3-difluoromethylphenyl, 4-difluoromethylphenyl, 2-trifluoromethylphenyl, 3-trifluoromethylphenyl, 4-trifluoromethylphenyl, 3,5-ditrifluoromethylphenyl, 2-6-ditrifluoromethylphenyl, naphth-1-yl, naphth-2-yl, pyridin-2-yl, pyridin-3-yl, pyridin-4-yl, furan-2-ilo, furan-3-ilo, tien-2-ilo and tien-3-ilo. Particular preference is given to metal dithiolene complexes of formula (I), wherein the radicals R1, R2, R3 and R4 all have the same meaning which is selected from the meanings defined herein, in particular the preferred ones. In another particular embodiment of the present invention, the IR-absorbing organic pigment contained in the microparticle-based composition of the present invention is selected from the group consisting of naphthalocyanine complexes of formula (II), (H) where M1is Cu, Fe, Mn, Pd, Pt, VO, Si(OR8)2, AI(R7) or Ga(R7), R5is H, F, OR9, SR9, NHR10, NR10R11, R6es H, F, OR9, SR9, NHR10, NR10R11, R7 is selected from the group consisting of Cl, OH and OR12; R8 is selected from the group consisting of C1-C12 alkyl, (C2H4O)m-R13 and phenyl; R9 is selected from the group consisting of C1-C12 alkyl, (C2H4O)m-R13 and phenyl; R10, R11 independently of each other, are selected from the group consisting of C1-C12 alkyl, (C2H4O)n-R13 and phenyl or R10, R11 together form a saturated 5- or 6-membered N-heterocyclic ring, which is optionally substituted with 1 or 2 methyl groups; R12 is selected from the group consisting of C1-C12 alkyl, (C2H4O)n-R13 and phenyl; R13es alkyl Ci-Ci2, yn, m independently of each other, are 0, 1, 2, 3 or 4. The M1 residue in the naphthalocyanine complex of formula (II) is preferably selected from the group consisting of Cu, Ga, Fe, Mn, Pd and Pt, in particular from Cu, Ga and Fe. Preferably, the radicals R5 and R6 in formula (II), independently of each other, are selected from the group consisting of H, F, OR9 and NHR10, in particular from H, F and OR9. According to a preferred embodiment of the invention, the radicals R5 and R6 have the same meaning. The radicals R7, R8, R9, R10, R10, R10, R10, nym have the following preferred meanings: R7 is OH or OR12, in particular OR12; R8 is alkyl Ci-Cso (C2H4O)m-R13, in particular alkyl Ci-Ce; R9 is alkyl Ci-Cso (C2H4O)m-R13, in particular (C2H4O)m-R13; R10 and R11, independently of each other, are Ci-Cs alkyl or (C2H4O)r-R13, more preferably C1-C6 alkyl or (C2H4O)n-R13 with ny R13 having the preferred meanings defined herein, or R10 and R11 together form a saturated 5 or 6-membered N-heterocyclic ring; R12es alkyl Ci-C8o (C2H4O)n-R13; R13 is Ci-C8 alkyl, in particular Ci-C8 alkyl; nym.independently among themselves, are 1, 2 or 3, in particular 2 or 3. In the microparticle composition of the present invention, the volume-weighted average particle diameter D(4.3) of the microparticles is frequently in the range of 2.0 to 14.0 pm, particularly in the range of 3.0 to 12.0 pm, preferably in the range of 3.5 to 11.0 pm, more preferably in the range of 4.0 to 10.0 pm and especially in the range of 4.5 to 9.5 pm determined by static light scattering. In the microparticle composition of the present invention, the D(v 0.5) of the microparticles is frequently in the range of 1.8 to 12.5 pm, particularly in the range of 2.8 to 11.0 pm, preferably in the range of 3.0 to 9.5 pm, more particularly in the range of 3.2 to 9.2 pm and especially in the range of 3.5 to 9.0 pm determined by static light scattering. In the microparticle composition of the present invention, the surface-weighted average mean diameter D(3.2) of the microparticles is frequently in the range of 1.6 to 12.5 pm, particularly in the range of 2.6 to 10.5 pm, preferably in the range of 2.8 to 9.2 pm, more particularly in the range of 3.0 to 9.0 pm and especially in the range of 3.2 to 8.8 pm determined by static light scattering. In the microparticle composition of the invention, the particle diameter D(v 0.1) of the microparticles is frequently at least 1.0 pm, in particular at least 2.0 pm, more particularly at least 2.4 pm and especially at least 2.7 pm, for example, in the range of 1.0 to 8.0 pm, in particular in the range of 2.0 to 7.0 pm, more particularly in the range of 2.4 to 6.0 pm and especially in the range of 2.7 to 5.5 pm, determined by static light scattering. In the microparticle composition of the invention, the particle diameter D(v 0.9) of the microparticles is frequently 20.0 pm at most, in particular 17.5 pm at most and especially 15.0 pm at most, for example, in the range of 4.0 to 20.0 pm, in particular 5.0 to 17.5 pm, more particularly in the range of 6.0 to 15.0 pm, determined by static light scattering. Frequently, the microparticle-based compositions of the present invention contain at least one dispersant, which can serve to stabilize the pigment particles against agglomeration during the production of the microparticle-based compositions of the present invention, but can also beneficially affect the properties of the microparticle-based compositions of the present invention, particularly with regard to their incorporation into printing inks. Suitable dispersants are known to experts. F. Pirrung and C. Auschra, in Macromolecular Engineering, Precise Synthesis, Materials Properties, Applications (ed. K. Matyjaszewski et al.), Chapter 4, Polymeric Dispersants, pp. 2135–2180, provide a general overview of the different types of polymeric dispersants, their polymeric architecture, and their properties. Suitable polymeric dispersants for the purpose of the invention are primarily organic polymers that are soluble or at least dispersible in water and have at least one polar group that provides the polymer's solubility or dispersibility in water, and frequently at least one anchoring group capable of adsorbing onto the surface of the pigment particle. Anchoring can be achieved through hydrogen bonding, dipole-dipole interactions, pi-pi interactions, London dispersion forces, Van der Waals forces, or a combination thereof. Preferably, the microparticle-based compositions of the present invention contain at least one dispersant selected to have one or more C2-C4 poly(oxyalkylene) groups. The polyoxyalkylene group imparts water solubility or dispersibility to the polymeric dispersant and serves to spherically stabilize the pigment particles against agglomeration in the aqueous phase. The molecular weight of the polyoxyalkylene groups can range from 200 to 5000 g / mol (number average), corresponding to a range of 3 to 110 oxyalkylene repeating units. Here and throughout the descriptive memory, the expressions “polyoxyalkylene group”, “polyalkylene oxide group” and polyalkylene glycol group are used as synonyms and refer to oligomeric or polymeric groups or residues, which are formed by alkylenoxy repeating units, in particular C2-C4 alkylene oxide repeating units, i.e., repeating units of the formula AO, where A is C2-C4 alkandiyl, such as 1,2-ethanediyl, 1,2-propanediyl, 1,2-butanediyl, 2,3-butanediyl or 1-methyl-1,2-propanediyl, and especially ethyleneoxy (CH2CH2O) and / or propylenoxy (CH(CH3)CH2O) repeating units. Polyoxyalkylene groups made from repeating C2C4 alkylene oxide units are hereafter referred to as poly(oxy-alkylene C2-C4) groups or poly-alkylene glycol C2-C4 groups, respectively.Polyoxyalkylene groups made from repeating units of ethylene oxide and / or propylene oxide are hereafter referred to as C2-C3 poly(oxyalkylene) groups or C2-C3 polyalkylene glycol groups, respectively. Polyoxyalkylene groups may be unprotected, for example, having a terminal OH group, or they may be capped, meaning they bear a terminal hydrocarbon radical attached to O, such as C1-C12 alkyl, C3-C12 alkyl, or benzyl. The appropriate anchoring groups in dispersants are in particular aromatic or partially unsaturated heterocyclic radicals, such as pyridinyl, pyrimidinyl, triazinyl, pyrazolyl, imidazolyl, imidazolinyl or triazolyl radicals, optionally substituted with 1, 2 or 3 radicals selected from C1-C22 alkyl, C2-C20 alkenyl, OH, amino (NH2), aminosulfonyl (SO2NH2) and carbamoyl (CONH2); aryl radicals, such as phenyl or naphthyl, wherein aryl carries at least one, for example, 1, 2 or 3 radicals selected from OH, amino (NH2), aminosulfonyl (SO2NH2) and carbamoyl (CONH2) and optionally 1, 2 or 3 radicals, selected from C1-C4 alkyl; long-chain fatty acid radicals that frequently have 8 to 22 carbon atoms, such as C8-C22 alkyl, C8-C22 alkenyl, C8-C22 alkadienyl; lactamyl groups, such as pyrrolidone, caprolactone or morpholinone groups; and urethane or urea groups, which includes imidazolinone groups and triazintrione groups. In particular, the microparticle-based compositions of the present invention contain at least one dispersant selected from the group consisting of non-ionic or anionic polymeric dispersants having a plurality of C2-C4 poly(oxyalkylene) groups (type I dispersant), acid polyethersters carrying at least one C2-C4 poly(oxyalkylene) group or mixtures thereof with C2-C4 poly(oxyalkylene) glycols and / or anionic surfactants (type II dispersant), and mixtures of a fatty acid-modified polyalkyleneimine and at least one anionic surfactant carrying at least one C2-C4 poly(oxyalkylene) group (type III dispersant). Examples of type I dispersants include non-ionic or anionic polymers having a polyurethane backbone, where the polyoxyalkylene groups are part of the backbone or side chains, and non-ionic or anionic polymers having a carbon backbone, where the polyoxyalkylene groups are present as side chains. A particular group of type I dispersants is selected from non-ionic comb polymers and anionic comb polymers having a carbon main chain, where polyoxyalkylene groups are present as side chains and mixtures thereof. In particular, the type I polymeric dispersant is selected from comb polymers having both repeating units bearing poly-C2-C4 alkyl ether groups and repeating units of monomers having an anchoring group, and mixtures of these with comb polymers having both repeating units bearing poly-C2-C4 alkyl ether groups and repeating units of acidic monomers. These comb polymers are frequently made from polymerized repeating units of ethylenically unsaturated M monomers comprising in polymerized form at least one monoethylenically unsaturated monomer having an anchoring group (monomer M1) or an acidic group (M1), a monoethylenically unsaturated monomer bearing a poly(oxyalkylene), in particular a poly(oxyalkylene C2-C4) group and especially a poly(oxyalkylene C2-C3) group (monomer M2), and optionally a non-ionic monomer M3 different from the same.For someone skilled in the art, it is evident that these types of polymers can be prepared by polymerizing the monomers M1, M2 and optionally M3, for example, by radical polymerization, or by subjecting a polymer made of polymers M1 and M3 to a polymer analogous reaction with OH-terminated C2-C4 poly(oxy-alkylene) ethers, in particular OH-terminated C2-C4 poly(oxy-alkylene) ethers, especially an OH-terminated monofunctional C2-C3 poly(oxy-alkylene) ether, provided that the M3 monomers have a functional group capable of undergoing an esterification or transesterification reaction, for example, a carboxyl group or a Ci-Ce alkoxycarbonyl group. The appropriate M1 monomers are N-vinyl lactams, such as N-vinylpyrrolidone, N-vinylcaprolactam and N-vinyl; vinyl or allyl substituted heterocycles, such as vinylpyridines, N-vinyl imidazole, N-vinyltriazole and N-vinylpyrazole; particular preference is given to vinylpyridines. Suitable MT monomers are monoethylenically unsaturated carboxylic acids, in particular monoethylenically unsaturated monocarboxylic acids having 3 to 6 carbon atoms, such as acrylic acid or methacrylic acid, and monoethylenically unsaturated dicarboxylic acids having 4 to 6 carbon atoms, such as maleic acid or itaconic acid. The appropriate M2 monomers are, for example, vinyl and allyl esters of poly(oxy-C2-C4 alkylene) ethers, which are also called poly-C2-C4 alkylene glycols and especially poly-C2-C3 alkylene glycols; acrylic acid esters with C2-C4 poly(oxy-alkylene) ethers, in particular with C2-C4 poly(oxy-alkylene) ethers and especially with C2-C3 poly(oxy-alkylene) ethers and methacrylic acid esters with C2-C4 poly(oxy-alkylene) ethers, in particular with C2-C3 poly(oxy-alkylene) ethers, which are hereinafter also referred to as C2-C4 poly-alkylene glycol (meth)acrylate and C2-C3 poly-alkylene glycol (meth)acrylate, respectively; maleic acid or fumaric acid diesters with C2-C4 poly(oxy-alkylene) ethers and especially with C2-C3 poly(oxy-alkylene) ethers. In the M2 monomers mentioned above, the C2-C4 poly(oxyalkylene) group may be unprotected, i.e., terminated with a hydroxyl group, or capped, i.e., terminated with a hydrocarbon radical attached to O, for example, a Ci-Ce alkyloxy group. For example, the poly(oxyalkylene) group is a Ci-Ce alkyl-terminated polyoxyethylene group or a Ci-Ce alkyl-terminated polyethylene glycol group, respectively a methyl-terminated polyoxyethylene group or a methyl-terminated polyethylene glycol group. The molecular weight of the poly(oxy-alkylene Cz-C^glycol group in type I dispersants can vary from 200 to 5000 g / mol, corresponding to 3 to 110 oxyalkylene repeating units. Among the M2 monomers mentioned above, acrylic acid esters with C2-C4 poly(oxyalkylene) ethers, particularly with C2-C3 poly(oxyalkylene) ethers, and methacrylic acid esters with poly(oxyalkylene) ethers, particularly with C2-C3 poly(oxyalkylene) ethers, are preferred. Special preference is given to C2-C4 polyalkylene glycol (meth)acrylates terminated with Ci-Ce alkyl, in particular to C2-C3 polyalkylene glycol (meth)acrylates terminated with G-Cs alkyl, and more particularly to Ci-Ce alkyl-terminated polyethylene glycol (meth)acrylates, especially the corresponding methyl-terminated polyalkylene glycol (meth)acrylates. The appropriate M3 monomers are, for example, Ci-Cs alkyl vinyl ethers and Ci-Cs alkyl allyl ethers; vinyl esters and allyl esters of Ci-Cs alkanoic acids, such as vinyl acetate or vinyl propionate; acrylic acid esters and methacrylic acid esters with C1-C12 alkanols, acrylic acid esters and methacrylic acid esters with C5-C12 cycloalkanols, in particular acrylic acid esters and methacrylic acid esters with Ci-Ce alkanols, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate; vinylaromatic hydrocarbons such as styrene and vinyltoluene: maleic acid diesters with C1-C12 alkanols, such as dibutyl maleate and dibutyl fumarate. Among the aforementioned M3 monomers, acrylic acid esters with C1-C12 alkanols and acrylic acid esters with C1-C12 alkanols, hereinafter referred to as C1-C12 alkyl (meth)acrylates, are preferred. Acrylic acid esters with Ci-Ce alkanols and acrylic acid esters with Ci-Ce alkanols, hereinafter referred to as C1C6 alkyl (meth)acrylates, are especially preferred. In particular, the type I dispersant comprises a nonionic comb polymer having a carbon, where the carbon main chain has both repeating units bearing a C2-C4 poly(oxy-alkylene) group and repeating units derived from vinylpyridine units or a mixture thereof with a comb polymer, where the carbon main chain has both repeating units bearing a C2-C4 poly(oxy-alkylene) group and repeating units derived from one or more MT monomers. Type II dispersants comprise at least one anionic polyether with one or more C2-C4 poly(oxyalkyl) groups, which is in particular a polyether of a C2-C4 poly(oxyalkyl) glycol, in particular a polyethylene glycol, with an aromatic dicarboxylic ester such as italic acid or terephthalic acid, and a diol component, which carries at least one carboxylic acid group. The anionic polyester may contain fatty acid units, in particular long-chain fatty acids having from 6 to 22 carbon atoms. The molecular weight of the C2-C4 poly(oxyalkylene) glycol groups in anionic polyesters of type II dispersants can vary from 200 to 5000 g / mol, corresponding to 3 to 110 oxyalkylene repeating units. The molecular weight of the polyester of type II dispersants can vary from 500 to 20000 g / mol, as determined by GPC. Type II dispersants may further comprise one or more poly(oxy-alkylene C2-C4) glycols, in particular polyethylene glycol or poly(ethylene-co-propylene) glycol, and / or an anionic surfactant, in particular an anionic surfactant bearing a sulfonate or sulfate group. Examples of anionic surfactants include alkylbenzenesulfonate salts, alkyl sulfate salts, and salts of sulfuric acid half-esters with C2-C4 alkoxylated fatty alcohols, in particular with ethoxylated or ethoxylated-copropoxylated fatty alcohols, particularly alkali metal salts and ammonium salts. Type III dispersants contain at least one oligo- or polyalkyleneimine, in particular at least one C2-C4 oligo- or polyalkyleneimine, which is modified with a fatty acid, in particular an oligo- or polyalkyleneimine modified based on an oligo- or polyalkyleneimine of the formula NH2-A-NH-(ANH)kA-NH2, where A is a C2-C3 alkylene and k is an integer from 0 to 50, in particular from 1 to 20. Suitable fatty acids for modification of the oligo- or polyalkyleneimine include C8-C22 alkanoic acids, C8-C22 alkenoic acids, and C8-C22 alkadienoic acids and mixtures thereof. The preferred modified oligo- or polyalkyleneminines preferably comprise at least 50% by weight, based on the total amount of modified C2-C4 oligo- or polyalkyleneminine, of compounds that can be described by the following formulas Illa, Illb, lile, IIId and lile: EITHER R' NH—A—NlA—N—La-N^^R' And HLHJk H O (Illa) (lllb) (Ule) NH-A—N—A—N HLH -A—NH2k (llld) R' where R' are the same or different and are selected from the group consisting of hydrocarbon radicals derived from a long-chain fatty acid and where R' is selected in particular from the group consisting of C7-C21 alkyl, C7-C21 alkenyl and C7-C21 alkadienyl; A is a C2-C3 alkylene, in particular 1,2-ethanendiyl; k is 0 to 50, in particular 1 to 20, m is k -1, that is, 0 to 49 and in particular 0 to 19. A person skilled in the art will readily appreciate that modified oligo- or polyalkyleneimines may also comprise compounds in which the additional nitrogen atoms of the polyalkyleneimine are modified by a fatty acid radical or an imidazoline radical as described for formulas (llb), (lle), and (lle). Particularly preferred modified oligo- or polyalkyleneimines comprise at least one compound of formula (lle) or a mixture thereof with one or more compounds of formulas (lla) or (llb), particularly a mixture in which the compounds of formulas (llb) and (lle) amount to at least 30% by weight, based on the total weight of the modified oligo- or polyalkyleneimines present in the dispersant. Type III dispersants further comprise one or more anionic surfactants bearing at least one C2-C4 poly(oxy-alkylene) group. Examples of such anionic surfactants include salts, in particular alkali metal salts and ammonium salts, of sulfuric acid half-esters with C2-C4 alkoxylated fatty alcohols, particularly ethoxylated or ethoxylated-copropoxylated fatty alcohols, and half-esters of an aliphatic dicarboxylic acid, such as maleic acid, fumaric acid, or succinic acid, with a C2-C4 alkoxylated fatty alcohol, particularly ethoxylated or ethoxylated-copropoxylated fatty alcohol. If present in the microparticle-based composition, the amount of dispersants is typically such that the weight ratio of the dispersant, calculated as solids, to the solid IR-absorbing organic pigment is in the range of 0.05:1 to 1:1, preferably in the range of 0.1:1 to 0.8:1, particularly from 0.1:1 to 0.5:1. According to a particular embodiment of the present invention, the microparticle-based compositions are in the form of an aqueous suspension. Such a suspension contains the microparticles as the dispersed phase and an aqueous medium as the continuous phase. The aqueous suspension can be obtained by the process for preparing a microparticle-based composition as described herein. Alternatively, it can be obtained by redispersing a solid microparticle-based composition, as described herein, in an aqueous medium. The term “aqueous medium” refers to the liquid phase of the composition and comprises an aqueous solvent and optionally compounds dissolved therein, for example, dispersants as previously mentioned, and if present, one or more conventional formulation aids, such as antifoaming agents or preservatives. The aqueous solvent of the aqueous suspension is water or a mixture of water with a water-miscible organic solvent, such as C1-C4 alkanols, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, or tert-butanol, C2-C5 alkanediols, and C3-C8 alkanetriols, preferably from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and 1,4-butanediol. Generally, the amount of water in the aqueous solvent is at least 50% by weight, in particular at least 80% by weight or at least 90% by weight, based on the aqueous solvent.The aqueous solvent may consist primarily of water, i.e., water constitutes at least 95% by weight of the total amount of solvent present in the suspension. The aqueous solvent may also be a mixture of the previously mentioned water-miscible organic solvent and water. In the latter case, the weight ratio of water to water-miscible organic solvent in the aqueous solvent is preferably in the range of 99:1 to 1:1; more preferably in the range of 50:1 to 3:1; and most preferably in the range of 20:1 to 4:1. Expressed differently, the amount of organic solvent may be from 1 to 50% by weight, more preferably from 2 to 25% by weight, and most preferably from 5 to 20% by weight, based on the total weight of the aqueous solvent. The aqueous suspension will normally contain the microparticles in an amount of at least 5% by weight, and the amount may be as high as 45% by weight or even greater, in each case based on the total weight of the aqueous suspension and calculated as the total amount of aminoplastic polymer and IR-absorbing pigment. Frequently, the aqueous suspension will contain the microparticles in an amount of 5 to 45% by weight, preferably 7 to 40% by weight, particularly 9 to 35% by weight, in each case based on the total weight of the aqueous suspension and calculated as the total amount of aminoplastic polymer and IR-absorbing organic pigment. The pigment concentration in the aqueous suspension will frequently be in the range of 1 to 40% by weight, particularly in the range of 2 to 25% by weight, more particularly in the range of 3 to 20% by weight, especially in the range of 4 to 15% by weight, based on the total weight of the aqueous suspension. If present, the concentration of one or more dispersants in the aqueous suspension is frequently in the range of 0.1 to 20% by weight, preferably 0.5 to 10% by weight, particularly 1.0 to 8% by weight, based on the total weight of the aqueous suspension of the microparticles. The aqueous compositions according to the invention may also contain common formulation aids, such as viscosity modifiers (thickeners), antifoaming agents, preservatives, buffers, inorganic dispersants, etc., which are commonly used in aqueous herbicide formulations. These aids may be incorporated into the aqueous suspension after step i) of the preparation process described herein has been carried out. The amount of additives will generally not exceed 10% by weight, and in particular 5% by weight of the total weight of the aqueous suspension. Suitable antifoaming agents for compositions according to the invention are, for example, silicone emulsions (such as, for example, Wacker Silicone SRE-PFL or Bluestar Silicones Rhodorsil®), polysiloxanes and modified polysiloxanes, including polysiloxane block polymers such as BASF SE's FoamStar® SI and FoamStar® ST products, long-chain alcohols, fatty acids, organofluorinated compounds, and mixtures thereof. Suitable preservatives for preventing microbial deterioration of the compositions of the invention include formaldehyde, alkyl esters of p-hydroxybenzoic acid, sodium benzoate, 2-bromo-2-nitropropane-1,3-diol, o-phenylphenol, thiazolinones such as benzisothiazolinone, 5-chloro-2-methyl-4-isothiazolinone, pentachlorophenol, 2,4-dichlorobenzyl alcohol, and mixtures thereof. Commercially available preservatives based on isothiazolinones are marketed, for example, under the brand names Proxel® (Arch Chemical), Acticide® MBS (Thor Chemie), and Kathon® MK (Rohm & Haas). If applicable, the compositions according to the invention, particularly aqueous suspensions, may include buffers for pH regulation. Examples of buffers are alkali metal salts of weak inorganic or organic acids, such as, for example, phosphoric acid, boric acid, acetic acid, propionic acid, citric acid, fumaric acid, tartaric acid, oxalic acid, and succinic acid. According to another particular embodiment, the microparticle-based compositions of the invention are in solid form. Such a solid composition contains the microparticles and optionally one or more dispersants, in particular the dispersants described herein as preferred. The solid compositions are particularly in the form of dispersible powders. The solid composition can be obtained from an aqueous suspension, which is formed primarily during the process of preparing the microparticle-based compositions as described herein, by removing the aqueous phase from the suspension. Removal of the aqueous phase can be achieved by separating it from the solid microparticles, for example, by centrifugation or filtration. Preferably, the aqueous phase is removed by an evaporation process, such as spray drying or freeze-drying. As described above, the method for producing the microparticle-based compositions of the present invention comprises a first step (i), where an aqueous suspension of the solid IR-absorbing organic pigment is provided, which also includes an aminoplastic precondensate of one or more amino compounds and one or more aldehydes. In this context, “IR-absorbing pigment” has one of the meanings defined herein, in particular one of the preferred meanings. The IR-absorbing pigment is preferably introduced in step i) in the form of a water-moistened pressed cake having a pigment concentration typically of 20 to 60% by weight, preferably 30 to 55% by weight, and particularly 35 to 50% by weight, based on the total weight of the pressed cake. The pressed cake can be prepared by mixing the pigment particles with a suitable amount of water in the absence of any dispersant or in the presence of a dispersant until a homogeneous material is obtained. Alternatively, the IR-absorbing pigment can be introduced in step i) in the form of particles that are largely dehydrated, for example, as a powder. Suitable aminoplastic precondensates are oligomeric or polymeric reaction products of one or more aldehydes, such as, for example, formaldehyde, acetaldehyde, propanal, glyoxal, or glutaraldehyde, with one or more amino compounds that usually have at least two primary amino groups, such as, for example, urea, thiourea, melamine, cyanoguanamine (= dicyandiamide), acetoguanamine, and benzoguanamine. The precondensates may be partially or fully etherified, meaning that the hydroxyl groups of the semi-amino units formed after the reaction of the primary amino groups are etherified with an alcohol, preferably a C2-C4 alkanol such as methanol, ethanol, propanol, n-butanol, 2-butanol, isobutanol, n-pentanol, or n-hexanol, and / or a C2-C4 alkanediol, such as ethylene glycol. Under curing conditions, the precondensates will form crosslinked aminoplastic polymers. Aminoplastic precondensates include, but are not limited to, melamine-formaldehyde condensation products (melamine-formaldehyde precondensates or MF precondensates), including fully or partially etherified MF precondensates, urea-formaldehyde precondensates (UF precondensates), thiourea-formaldehyde precondensates (TUF precondensates), melamine, urea, and formaldehyde precondensates (MUF precondensates), including fully or partially etherified MUF precondensates, melamine, thiourea, and formaldehyde precondensates (MTUF precondensates), including fully or partially etherified MTUF precondensates, urea-glutaraldehyde precondensates, and benzoguanamine-formaldehyde precondensates. dicyandiamide-formaldehyde precondensates and urea-glyoxal precondensates. Suitable aminoplastic precondensates for microencapsulation are known and can be found, inter alia, in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd edition, vol. 2, pp. 440-469, the above technique cited in the introductory part, documents US 4,918,317, EP 26914, EP 218887, EP 319337, EP 383,337, EP 415273, DE 19833347, DE 19835114 and WO 01 / 51197. Suitable precondensates are commercially available, for example, Cymel types such as, but not limited to, Cymel® 303, 327, 328 or 385 (etherified melamine-formaldehyde resins from Cytec), Maprenal® types such as, but not limited to, Maprenal® MF 900w / 95, MF 915 / 75IB, MF 920 / 75WA, MF 921w / 85WA (etherified melamine-formaldehyde resins from Ineos), Kauramin® types from BASF SE such as, but not limited to, Kauramin® 783, Kauramin® 792 or Kauramin® 753 (melamine-formaldehyde resins), Kauramin® 620 or Kauramin® 621 (melamine-urea-formaldehyde resins), Kaurit® types from BASF SE,such as, but not limited to, Kaurit® 210, 216, 217, 220, 270, 285, 325 (aqueous solution of urea-formaldehyde resins), Luracoll® types, such as Luracoll® SD (etherified melamine-formaldehyde resins), Luwipal® types, such as, but not limited to, Luwipal® 063, Luwipal® 069 (etherified melamine-formaldehyde resins), or Plastopal® types, such as, but not limited to, Plastopal® BTM, Plastopal® BTW (etherified urea-formaldehyde resins). In suitable urea-formaldehyde or thiourea-formaldehyde precondensates, the molar ratios of urea or thiourea to formaldehyde are generally in the range of 1:0.8 to 1:4, particularly in the range of 1:1.5 to 1:4, especially in the range of 1:2 to 1:3.5. In suitable melamine-formaldehyde precondensates, which may be totally or partially etherified, the molar ratios of melamine to formaldehyde are generally in the range of 1:1.5 to 1:10, particularly in the range of 1:3 to 1:8, preferably in the range of 1:4 to 1:6. In suitable melamine-(thio)urea-formaldehyde precondensates, which may be totally or partially etherified, the molar ratios of melamine + urea or thiourea to formaldehyde are generally in the range of 1:0.8 to 1:9, particularly from 1:2 to 1:8, preferably in the range of 1:3 to 1:6. The molar ratio of urea or thiourea to melamine is usually found in the range of 5:1 to 1:50 and particularly in the range of 3:1 to 1:30. The precondensates can be used in the form of etherified amino-aldehyde precondensates. In these etherified precondensates, the methylol groups are formed by the reaction of the amino groups with formaldehyde and an alkanol or an alkanediol, particularly a C2-C4 alkanol such as methanol, ethanol, n-propanol, or n-butanol, or a C2-C4 alkanediol such as ethylene glycol. The degree of etherification of these resins can be adjusted by the molar ratio of amino groups to alkanol, which is typically in the range of 10:1 to 1:10, preferably in the range of 2:1 to 1:5. The precondensates are specifically selected from the group consisting of melamine-formaldehyde precondensates, including wholly or partially etherified melamine-formaldehyde precondensates, melamine-urea-formaldehyde precondensates, and wholly or partially etherified melamine-formaldehyde precondensates, and mixtures thereof. Specifically, the precondensate is a wholly or partially etherified melamine-formaldehyde condensate, which may contain small amounts, for example, 1 to 20 mol% (based on melamine), of urea. The aqueous suspension according to step i) can be obtained by incorporating the particulate pigment and the aminoplastic precondensate into an aqueous medium, such as water. Preferably, the aqueous suspension further contains at least one dispersant, which is preferably selected from the dispersants described herein as optional components of the microparticle-based compositions of the invention, particularly those described as preferred. The aqueous suspension may contain the dispersant in an amount representing a portion or the total amount intended to be included in the final microparticle-based composition. The aqueous suspension provided in step i) may contain additional auxiliaries intended for the microparticle-based compositions of the invention, such as, in particular, one of the antifoaming agents described herein. In one embodiment of the present invention, a portion or the entire amount of the antifoaming agent intended for inclusion in the final microparticle-based composition is already present in the suspension. The aqueous suspension contains the aminoplastic precondensate in an amount that is normally in the range of 20 to 65% by weight, particularly 25 to 57% by weight and especially 27 to 52% by weight, based on the total weight of the aminoplastic precondensate and the IR-absorbing organic pigment and calculated as solid organic matter. In step i), the pigment is present in the suspension in particulate form. The particle size distribution of the IR-absorbing organic pigment particles is typically characterized by having a particle size smaller than the particle size of the microparticles containing the solid IR-absorbing organic pigment particles, which are surrounded or embedded by an aminoplastic polymer. Frequently, the particle size distribution of the IR-absorbing organic pigment particles is characterized by having a D(v, 0.5) value of 0.8 pm at most, particularly 0.5 pm at most, and especially 0.3 pm at most, for example, in the range of 10 to 800 nm, particularly from 20 to 500 nm, and more specifically in the range of 20 to 300 nm, as determined by static light scattering.However, in suspension, the IR-absorbing organic pigment particles can form loose agglomerates, and therefore the apparent particle size may be larger. Nevertheless, the particle size distribution of the primary IR-absorbing organic pigment particles that form the agglomerate is typically characterized by having a D(v, 0.5) within the ranges mentioned above. IR-absorbing pigments suitable for the microparticle-based compositions of the invention can be obtained, for example, from chemical synthesis or commercial sources that already have an appropriate particle size distribution and a mean particle diameter D(v 0.5) within the aforementioned ranges. If the pigment particles to be used are too coarse, the particle size can be reduced by employing established particle communication methods, including in particular communication techniques involving water or an organic solvent and grinding media such as beads or inorganic salts. Suitable methods and devices are known and have been described, for example, in Perry's Chemical Engineers' Handbook, 7th ed. McGraw Hill 1997, pp. 20-31 to 20-38, and the literature cited therein, and are commercially available, for example, from Netzsch Feinmahltechnik, FHZ GmbH, Hosokawa-Alpine AG, and Willy A.Bachofen AG Maschinenfabrik, Coperion y Bühler GmbH. The IR-absorbing pigment present in the suspension from step i) can be deagglomerated during, or preferably before, step ii). This breaks down the pigment particle agglomerates within the suspension. Deagglomeration can be achieved by applying strong shear forces to the suspension, for example, using a disperser or homogenizer, such as a disc homogenizer or a rotor-stator homogenizer, or by applying ultrasound. Suitable homogenizers are well-known and commercially available, for example, from Netzsch Feinmahltechnik or IKA-Werke GmbH & Co. KG. The application of ultrasound for particle deagglomeration in the liquid phase has been frequently described, for example, in WO 99 / 32220 or by U Teipel et al., Int. J. Mineral Processing Vol. 74, Supplement (2004), S183-S190.Deagglomeration is typically continued until a particle size distribution and mean particle diameter D(v 0.5) are obtained within the aforementioned intervals. The aqueous suspension is prepared in step i) under conditions that prevent any significant polycondensation of the aminoplastic precondensate at this stage. This is achieved particularly by adjusting the pH to at least pH 6, for example, from pH 6 to pH 9. To obtain a homogeneous mixture, the components of the aqueous suspension, i.e., the pigment particles, typically a detergent, an aminoplastic precondensate, and optionally auxiliaries, such as an antifoaming agent, are combined and vigorously stirred, typically using a high-performance mixer, such as disc dispersers using toothed discs shaped to high peripheral tip speeds (e.g., from Vollrath GmbH), Ultra-turrax dispersers (IKA®-Werke GmbH & Co), and / or ultrasonic devices, such as ultrasonic tips.Preferably, the mixture is dispersed with a disc disperser or, alternatively, it is initially dispersed with an Ultraturrax disperser and then treated with a cooled ultrasonic tip. In step ii) of the method of the invention for producing the microparticle-based compositions of the invention, the polycondensation of the aminoplastic precondensate in the aqueous suspension obtained in step i) is carried out in the presence of one or more surfactants, preferably selected from the dispersants described herein as optional components of the microparticle-based compositions of the invention. Therefore, depending on the amount of such dispersant already added to the suspension in step i), an additional amount of dispersant can be added in step i) up to the total amount of dispersant intended for inclusion in the final microparticle-based compositions. Preferably, however, the amount of dispersant intended for inclusion in the final composition is already added in step i). Accordingly, it is preferred that the one or more surfactants contained in the aqueous suspension in which the polycondensation is carried out in step ii) be selected from the dispersants described herein as optional components of the microparticle-based compositions according to the present invention. The one or more surfactants, i.e., especially the one or more dispersants defined herein, are typically used in such quantity in step ii) that the weight ratio of the surfactant to the solid IR-absorbing organic pigment is in the range of 0.05:1 to 1:1, preferably in the range of 0.1:1 to 0.8:1, and particularly from 0.1:1 to 0.5:1. The concentration of the aminoplastic precondensate in the aqueous suspension subjected to polycondensation in step ii) is frequently in the range of 0.5 to 30% by weight, preferably 1.0 to 25% by weight, in particular 2.0 to 20% by weight, based on the total weight of the suspension. The concentration of the pigment in the aqueous suspension subjected to polycondensation is usually in the range of 1 to 40% by weight, particularly in the range of 2 to 25% by weight, more particularly in the range of 3 to 20% by weight, especially in the range of 4 to 15% by weight of the total weight of the suspension. The polycondensation of the aminoplastic precondensate can be carried out in a well-known manner, for example, by adjusting the pH of the suspension obtained in step i) to a maximum of 5.5 and heating it to a specific reaction temperature, which are suitable conditions for initiating and carrying out the polycondensation. During the polycondensation, the aminoplastic precondensate is converted into a water-insoluble aminoplastic resin, which precipitates from the aqueous phase and preferentially deposits on the surface of the solid pigment particles, thus encrusting or surrounding the pigment particles to obtain pigment-polymer particles. According to the invention, the aminoplastic polycondensation is carried out at a pH of pH 5.5 at most, in particular at a pH of pH 5 at most, especially at a pH of pH 4 at most, for example, in the pH range 0 to 5, more particularly in the pH range 1 to 4 or in the pH range 2 to 4. The pH of the aqueous suspension is typically adjusted by adding suitable amounts of an organic or inorganic acid, such as sulfuric acid, hydrochloric acid, phosphoric acid, a carboxylic acid (including alkanoic, alkanedioic, or hydroxycarboxylic acids such as formic, acetic, propionic, oxalic, malic, or citric acids), or alkyl- or arylsulfonic acids such as methanesulfonic or toluenesulfonic acid. Preferably, the acid catalyst is selected from the group consisting of formic acid, sulfuric acid, methanesulfonic acid, and hydrochloric acid, and particularly formic acid. It is preferred, but not required, that at least a portion, particularly a majority, of the acid be present in the aqueous suspension before it is heated to the reaction temperature. Preferably, the polycondensation of the aminoplastic precondensate is carried out at an elevated temperature, in particular at least 50°C, and more specifically at least 60°C, and can be as high as 100°C. Preferably, the temperature at which the polycondensation of the aminoplastic precondensate is carried out does not exceed 95°C, in particular 90°C, and is preferably in the range of 50 to 95°C, in particular in the range of 60 to 90°C or in the range of 70 to 90°C. It may be possible to initiate the aminoplastic polycondensation at a comparatively low temperature, for example, in the range of 40 to 60°C, and then complete the polycondensation reaction at a higher temperature of, for example, 60 to 95°C or 70 to 90°C. The time to complete the polycondensation can vary, depending on the reactivity of the precondensate, the temperature and the pH of the aqueous suspension, and can be from 0.3 to 10 h, in particular from 0.5 to 5 h. The aqueous suspension thus obtained from the pigment-polymer particles can be neutralized by the addition of a base. Preferably, the pH of the suspension is adjusted to at least 6, for example, a pH in the range of 6 to 10, particularly in the range of 6.5 to 9.0. Suitable bases include, but are not limited to, organic amines, particularly water-soluble amines such as mono-, di-, and triethanolamine. However, inorganic bases such as potassium hydroxide or sodium hydroxide may also be used. However, for the purpose of the invention, such neutralization is not required. Aqueous suspensions of pigment-polymer particles, obtainable by the process of the present invention, qualify as microparticle-based compositions of the invention. In these aqueous suspensions, the pigment-polymer particles contain a pigment and an aminoplastic resin, which surrounds or encrusts the pigment. Aqueous suspensions of pigment-polymer particles further contain one or more surfactants as previously defined, which are preferably selected from the dispersants described in detail herein, such as in particular those mentioned as preferred. From the aqueous suspensions obtained by the process described herein, the pigment-polymer particles can be isolated, for example, by filtration or centrifugation, or the aqueous suspension can be spray-dried, granulated, or freeze-dried to obtain a solid composition in the form of a powder or granules. The solid composition can then be resuspended or formulated using formulation aids as described herein, such as viscosity modifiers (thickeners), antifoaming agents, preservatives, buffers, inorganic dispersants, and others commonly used in aqueous formulations. The microparticle compositions of the present invention, in the form of an aqueous suspension of the microparticles, as well as in the form of a solid composition of the microparticles, such as powders, can be used for printing ink formulations, which are particularly suitable for security printing. Security features, for example, for security documents, can be classified as "covert" and "overt." The protection provided by covert security features is based on the concept that these features are hidden; they generally require specialized equipment and expertise for detection. In contrast, "overt" security features are easily detectable by the unaided human senses. For example, such features may be visible and / or detectable through touch while remaining difficult to produce and / or copy. The printing of a "covert" security feature typically involves printing an image onto a substrate that is otherwise invisible or undetectable under ambient conditions and that can be made visible or detectable by applying a suitable stimulus.The stimulus can be, for example, electromagnetic radiation or heat. Specifically, the printing formulations of the present invention allow a security image to be coated or printed onto a substrate. Since the printing formulation of the invention comprises IR-absorbing pigments, these pigments also form part of the image coated or printed on the substrate. By using devices capable of measuring IR radiation, it is possible to detect the otherwise undetectable image based on the degree to which IR radiation is absorbed, particularly wavelengths radiated in the range of 750 to 1100 nm, especially in the range of 790 to 1100 nm. In this way, the specific security image on the substrate can be identified. The printing formulations of the invention are particularly suitable for this type of security printing, as they allow security images that exhibit radiation reflectance of wavelengths in the range of 750 to 1100 nm, especially 790 to 1100 nm, which is reduced by at least 40%, and in particular at least 50%, compared to the blank substrate. The printing ink formulations of the present invention, particularly those applicable to security printing, contain, in addition to a microparticle-based composition as defined herein, a binder which, in principle, can be selected from any binder known in the art that is suitable for formulating printing inks. More particularly, the binders for the printing ink formulations of the invention are selected from binders that are radiation-curable, heat-dryable, or oxidatively dry, and consequently result in ink formulations that are radiation-curable, heat-dryable, or oxidatively dry. Oxidatively drying binders and the oxidatively drying inks obtained from them are particularly preferred in the context of the invention. Examples of radiation-curable binders, particularly UV-curable binders, are binders containing oligomers and monomers with ethylenically unsaturated double bonds. The oligomers are typically selected from polyether (meth)acrylates (i.e., polyethers having acrylic or methacrylic groups), polyester (meth)acrylates (i.e., polyesters having acrylic or methacrylic groups), and urethane (meth)acrylates (i.e., oligomers having a (poly)urethane structure and acrylic or methacrylic groups), for example, reaction products of polyisocyanates with hydroxyfunctionalized acrylic or methacrylic compounds and mixtures thereof. Preferably, the oligomers are polyester acrylates, urethane acrylates, and mixtures thereof.The monomers are typically selected from acrylic acid esters with mono- to tetrahydric (cyclo)aliphatic alcohols, such as trimethylolpropane diacrylate, trimethylolpropane triacrylate, ethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, phenoxyethyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate, 4-tert-butylcyclohexyl acrylate, 4-hydroxybutyl acrylate, and trimethylolformal monoacrylate (5-ethyl-1,3-dioxan-5-yl) methyl ester of acrylic acid). Examples of thermally or oxidatively drying binders are alkyd resins, such as long-oil alkyd resins, polyamide resins, (meth)acrylic resins, resins of R7M?nn / i ζηζ / E / γ polyurethane, phenolic resins, vinyl resins, rosin-modified maleic resins, and varnishes prepared by cooking a resin, such as an alkyd, polyurethane, or phenolic resin, with an oxidative drying oil, such as tung oil, linseed oil, poppy seed oil, or perilla oil, as well as mixtures of these resins and varnishes. The aforementioned resins and varnishes are well known and described in more detail, for example, by R. van Gorkum et al., Coordination Chemistry Review 249 (2005) 1709-1728; J.F. Black, J. Am. Chem. Soc., 1978, 100, 527; J. Mallégol et al., Prog. Org. Coatings 39 (2000) 107-113, The Printing ink manual, RH Leach and RJ Pierce, Springer edition, 5th edition and commercially available, for example, from Epple Druckfarben AG. The security ink comprising the microparticles described herein may be an oxidative drying security ink comprising, in addition to the microparticles and the oxidative drying binder(s), from approximately 0.01 to approximately 10% by weight, based on the total weight of the oxidative drying security ink, of one or more dryers, or a UV-Vis curable security ink comprising, in addition to the microparticles and the UV-Vis curable binder(s), from approximately 0.1 to approximately 20% by weight, based on the total weight of the UV-Vis curable security ink, of one or more photoinitiators or a heat-drying security ink comprising, in addition to the microparticles and the heat-drying binder(s), from approximately 10 to approximately 90% by weight, based on the total weight of the heat-drying security ink, of one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, or a combination of the security inks mentioned above. Particular preference is given in this document to printing ink formulations comprising at least one oxidative drying binder specially selected from alkyd resins, such in particular as long oil alkyd resins, polyamide resins, (meth)acrylic resins, vinyl resins, rosin-modified maleic resins, varnishes made by cooking an alkyd, polyurethane or phenolic resin with tung or linseed oil, optionally followed by dissolution in an organic solvent such as mineral oil, as well as mixtures of these resins and varnishes. The printing ink formulations of the invention typically comprise auxiliaries and additional components that are commonly included in inks, such as, for example, pigments and dyes, fillers, for example, alumina, calcium carbonate or kaolin, dyes, for example, cobalt carboxylate or manganese carboxylate, solvents, surfactants, waxes, UV stabilizers, photoinitiators, antioxidants, emulsifiers, sliding agents, etc. In the following formulations A to D, they serve as specific examples of the printing ink formulations of the present invention, where the individual components have the meanings defined herein, in particular the preferred meanings. Formulation A: an oxidative drying intaglio ink formulation: 10-30% by weight 0-15% by weight 1-10% by weight oxidative drying ream; pigment; microparticle composition of the invention comprising IR-absorbing organic pigment, preferably in the form of a solid composition of the microparticles; 10-50% by weight 5-20% by weight 0.1-3% by weight 1-7% by weight 1-10% by weight 0.1-5% by weight filler; solvent; dryer; wax; surfactant; additives, for example, slip agent, antioxidant or stabilizer. Formulation B: a UV-curable intaglio ink formulation: 20-35% by weight 10-30% by weight 0-20% by weight 1-10% by weight oligomers; monomers; pigment; microparticle composition of the invention comprising IR-absorbing organic pigment, preferably in the form of a solid composition of the microparticles; 10-50% by weight 1-10% by weight 1-3% by weight 1-5% by weight filler; photoinitiator; UV stabilizer; additives, for example, emulsifier. Formulation C: a heat-setting or heat-drying intaglio ink formulation: 25-35% by weight 0-5% by weight 1-10% by weight heat-curing resin; pigment; microparticle composition of the invention comprising IR-absorbing organic pigment, preferably in the form of a solid composition of the microparticles; 45-50% by weight 10-15% by weight 0.5-2% by weight 1-5% by weight filler; solvent; dryer; wax. Formulation D: an oxidative drying offset ink formula: 20-40% by weight 30-50% by weight varnish I: oxidative drying resin, such as an alkyd resin; varnish II: oxidative drying resin prepared by cooking a resin, such as an alkyd, polyurethane or phenolic resin, in particular a phenolic resin, with a drying oil, such as tung oil; 10-20% by weight 1-10% by weight pigment; microparticle composition of the invention comprising IR-absorbing organic pigment, preferably in the form of a solid composition of the microparticles; 1-7% by weight 0.1-0.5% by weight 1-5% by weight wax; antioxidant; drier. The present invention also relates to a method for producing a security feature or security document, comprising applying a printing ink formulation to a substrate by a printing process. The printing ink formulations of the invention can be applied by a printing process preferably selected from the group consisting of offset printing processes, gravure printing processes, screen printing processes, copperplate intaglio printing processes, flexographic printing processes, and letterpress printing processes; more preferably by offset printing processes and copperplate intaglio printing processes. The aforementioned printing techniques are well known to the experts. In this context, the expression “security feature” is in particular a specific image that is printed on a substrate; and the term “substrate” means any object that is intended to be provided with a security feature, or that is intended to be made into a security document by applying the ink formulation to produce a security feature.The term “security document” means any document intended to be protected against counterfeiting. Such security documents include, in particular, valuable documents and commercial goods of value. Typical examples of valuable documents include, for instance, banknotes, deeds, tickets, checks, vouchers, revenue stamps and tax labels, agreements and the like; identity documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, transaction cards, access documents or cards, admission tickets, public transport tickets or titles and the like, preferably banknotes, identity documents, documents conferring rights, driver's licenses, and credit cards.The term “commercial good of value” refers to packaging materials, particularly for cosmetics, nutraceuticals, pharmaceuticals, alcohols, tobacco products, beverages or food, electrical / electronic goods, textiles, or jewelry—that is, items that must be protected against counterfeiting and / or illegal reproduction to guarantee the contents of the packaging, such as genuine medicines. Examples of such packaging materials include labels, such as authentication mark labels, tamper-evident labels, and seals. It is noted that the disclosed substrates, documents of value, and commercial goods of value are provided for illustrative purposes only and do not restrict the scope of the invention. Alternatively, the printing ink formulation of the invention comprising microparticles including an IR-absorbing organic pigment can be printed onto an auxiliary substrate such as, for example, a security thread, security strip, foil, decal, window, or label and subsequently transferred to a security document in a separate step. In addition to their use for protecting and authenticating security documents, as previously described, the printing ink formulations of the present invention can also be used for decorative purposes by applying the formulations to objects or items to be decorated. Examples of such objects or items typically include luxury goods, cosmetic packaging, automotive parts, household appliances, furniture, and nail polish. Accordingly, the present invention also relates to security documents, as well as to decorative objects comprising a substrate, on which a printing ink formulation of the invention has been applied by means of a printing process. Figure 1: The diagram shows the relative decrease in absorption calculated from the referral of a measured print to the maximum absorption of the printing inks of the invention and comparatives of application example 3. The particle size distribution (PSD) was determined by laser diffraction using a Malvern Mastersizer 2000 in accordance with the European standard ISO 13320:2009 EN. The data were processed according to Mie theory using software with a “universal model” provided by Malvern Instruments. The important parameters are, in particular, the following values: D(v 0.5), D(v 0.9), D(v 0.1), D(3.2), and D(4.3), where D(v 0.5), D(v 0.9), D(v 0.1), D(3.2), and D(4.3) are as defined herein. Aminoplastic precondensate A: 70% by weight aqueous solution of a methylated melamine formaldehyde precondensate: Luracoll® SD, BASF SE. Pigment A: IR absorbing nickel-dithiolene complex pigment of formula (I), where R1, R2, R3 and R4 are aryl: CAS name [nickel (II), bis(diphenílimídazolídíntrithione-KS4, kS5-), (SP-4-1)-]. Pigment B: IR-absorbing copper naphthalocyanine complex pigment of formula B-6 of document EP 3067216. Pigment C: IR-absorbing nickel ditlolene complex pigment of formula (I), where R1, R2, R3 and R4 are methyl. Pigment D: IR-absorbing nickel dichloroethylene complex pigment of formula (I), where R1, R2, R3 and R4 are [propio]. Dispersant A: Commercially available type I dispersant (40 wt% aqueous solution of copolymer having repeating units of butyl acrylate, methyl polyethylene oxide acrylate and vinylpyridine, prepared according to example A6 of WO 2006 / 074969). Dispersant B: Type III dispersant (water containing a mixture of a fatty acid-modified pentamethylenehexamine and a maleic acid-ethoxylated fatty acid hemiester, with a solids content of 97% by weight). Antifoam agent A: modified polydimethylsiloxane: Foamstar® SL 2280, BASF SE Preparation examples: Example 1a: 29.91 g of a wet cake of pigment A (46.8% pigment by weight) was mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A, as well as 12.25 g of aminoplastic precondensate A in 108.53 g of water. This mixture was pre-dispersed using an Ultra-Turrax and then ultrasonically treated with an ultrasonic tip under ice cooling for 10 minutes. Subsequently, 4 g of an aqueous formic acid solution (20% by weight) was added. The mixture was stirred for 1 hour at room temperature. The temperature was then increased to 80°C for 1 hour, held at 80°C for 2 hours, and then cooled to room temperature. An encapsulated pigment dispersion was obtained. The characteristic values ​​of the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Next, this dispersion was dried and yielded a fine powder. Examples 1b and 1c are repetitions of example 1a. The characteristic values ​​of the particle size distribution are given in Table 1. Example 2: 33.12 g of a wet cake of pigment A (46.8% pigment by weight) were mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A, as well as 9.19 g of aminoplastic precondensate A in 105.82 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 3: 32.05 g of a wet cake of pigment A (46.8% pigment by weight) were mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A, as well as 10.21 g of aminoplastic precondensate A in 106.72 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 4: 30.98 g of a wet cake of pigment A (46.8% pigment by weight) were mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A as well as 11.23 g of aminoplastic precondensate A in 107.63 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for particle size distribution and relative pigment to aminoplast content are given in Table 1. Example 5: 28.85 g of a wet cake of pigment A (46.8% pigment by weight) were mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A, as well as 13.27 g of aminoplastic precondensate A in 109.5 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 6: 27.78 g of a wet cake of pigment A (46.8% pigment by weight) were mixed with 20 g of dispersant A and 0.4 g of antifoaming agent A, as well as 14.29 g of aminoplastic precondensate A in 109.5 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 7: 155.44 g of a wet cake of pigment A (38.60 wt% pigment) was mixed with 25 g of dispersant A and 2.0 g of antifoaming agent A, as well as 81.66 g of aminoplastic precondensate A in 449.55 g of water. This mixture was dispersed using a disc disperser at a stirring speed of 10,000 rpm. Subsequently, 20 g of a 20 wt% formic acid solution was added. The mixture was stirred for 1 hour at room temperature. This mixture was then treated in the same manner as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 8: 29.91 g of a wet cake of pigment A (46.8 wt% pigment) were mixed with 5.0 g of dispersant A and 0.4 g of antifoaming agent A, as well as 12.25 g of aminoplastic precondensate A in 63.55 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Example 9: 33.10 g of a wet cake of pigment A (42.3% pigment by weight) were mixed with 8.24 g of dispersant B and 0.4 g of antifoaming agent A, as well as 12.25 g of aminoplastic precondensate A in 63.55 g of water. This mixture was then treated in the same way as described in Example 1a. Characteristic values ​​for the particle size distribution and the relative amount of pigment to aminoplast are given in Table 1. Table 1: P / A1* D(v 0.1) [pm] D(v 0.5) [pm] D(v 0.9) [pm] D(3.2) [pm] D(4.3) [pm] Example 1a 2.3 4.17 6.35 9.57 6.02 6.66 Example 1b 2.3 4.16 6.36 9.60 6.01 6.67 Example 1c 2.3 3.79 5.68 8.43 5.40 5.94 Example 2 3.4 2.53 3.96 6.41 3.76 4.25 Example 3 3.0 2.80 4.91 8.55 4.50 5.35 Example 4 2.6 2.84 4.95 8.63 4.54 5.39 Example 5 2.1 3.95 5.97 8.93 5.67 6.25 Example 6 1.9 4.11 6.22 9.30 5.90 6.51 Example 7 1.5 4.41 6.77 10.24 6.49 7.10 Example 8 2.3 2.17 3.37 5.56 3.22 3.66 Example 9 2.3 5.40 8.85 14.16 8.2 9.41 1) P / A: Pigment to aminoplast weight ratio calculated in the final particle Microparticle-based compositions of pigments B, C, and D can be prepared by analogy with the procedures described in Examples 1a to 9. Application examples: Application Example 1: Preparation of the ink formulation for offset printing (general procedure): One part of the solid composition of powdered microparticles of the invention was incorporated into nine parts of a commercial oxidative-drying offset varnish. The mixture was homogenized using a three-roll mill. Application example 2: Comparison of prints with adjusted IR absorption: An offset ink formulation according to the invention was prepared, consisting of 10 wt% of the solid microparticle composition of Example 1a in a commercial oxidative-drying offset varnish (Glanzdrucklack 1188, Epple AG) as previously described. The ink was printed on paper (ARCO II / II paper; Fogra Forschungsgesellschaft Druck e.V.) using offset printing equipment (Prüfbau). A suitably prepared ink formulation including 4 wt% of the unencapsulated pigment A was selected as a comparison formulation and printed because it was found to produce an offset paper print that had almost the same IR emission in the 750–1100 nm wavelength range as a print of the ink formulation of the invention when measured with an NIR spectrometer (Datacolor 45IR) immediately after printing. Both prints were remeasured after 20 days.The results obtained showed that after this period the increase in remission of prints prepared with the comparative ink is 25% greater than the increase in remission of prints prepared with the ink of the invention (measured at maximum ink absorption). Application example 3: Comparison of prints prepared with inks that have the same pigment concentration: An offset ink formulation was prepared according to the invention of the solid microparticle composition of Example 1c in a non-commercial oxidative-drying offset varnish as previously described. The pigment concentration was 4% by weight. A comparative ink was prepared similarly, but using an unencapsulated pigment A with a pigment concentration of 4%. The inventive ink formulation and the comparative ink formulation were printed on paper (APCO II / II paper; Fogra Forschungsgesellschaft Druck e.V.) using offset printing equipment (Prüfbau) such that an ink concentration of 2 g / m² (4% pigment loading) of paper was obtained in each case. IR emissions in the 750–1100 nm wavelength range from the prints were monitored for 20 days using an NIR spectrometer (Datacolor 45IR).The relative decrease in absorption measured at the maximum absorption of the ink (calculated from the reference) is shown in Figure 1. Application Example 4: Comparison of prints prepared with inks that have the same pigment concentration: An oxidative-drying offset ink formulation according to the invention was prepared from the solid microparticle composition of Example 7 in a commercial oxidative-drying offset varnish (Matt 2154, Epple AG) as previously described. The pigment concentration was 4% by weight. A comparative ink was prepared similarly, but using unencapsulated pigment A with a pigment concentration of 4%. The inventive ink formulation and the comparative ink formulation were printed on paper (APCO II / II paper; Fogra Forschungsgesellschaft Druck eV) using offset printing equipment (Prüfbau) such that in each case an ink load of 1 g / m² (4% pigment concentration) of paper was obtained. IR emissions in the wavelength range of 750 to 1100 nm from the prints were measured with an NIR spectrometer (Datacolor 45IR) directly after printing and again after 6 days.During this period, the remission of the print obtained with the comparison ink had increased by 37% compared to the initial measured remission, and the print obtained with the ink of the invention by only 7%.

Claims

1. A pigment composition based on microparticles of an IR-absorbing organic pigment, which is a polyunsaturated polycyclic organic compound or metallic organo-compound having a principal absorption maximum in the range of 750 to 1100 nm, wherein the microparticles of the pigment composition contain the IR-absorbing organic pigment as solid particles, which are surrounded or embedded in an aminoplastic polymer, which is a polycondensation product of one or more amino compounds and one or more aldehydes, wherein the microparticle-based pigment composition is characterized by a volume-based particle size distribution, determined by static light scattering according to ISO 13320: 2009 EN, having a volume mean value D(4.3) in the range of 1.0 to 15.0 pm, where the amount of aminoplastic polymer in the microparticle composition is 15 to 50% by weight, based on the total weight of the aminoplastic polymer and the IR-absorbing organic pigment, and the amount of the IR-absorbing organic pigment is 50 to 85% by weight, based on the total weight of the aminoplastic polymer and the IR-absorbing organic pigment.

2. The composition according to claim 1, wherein the aminoplastic polymer is a melamine formaldehyde resin.

3. The composition according to any of the preceding claims, wherein the IR-absorbing organic pigment is selected from the group consisting of metal dithiolene complexes, phthalocyanine pigments, naphthalocyanine pigments, rylene pigments, polymethine pigments, anthraquinone pigments, and mixtures thereof.

4. The composition according to claim 3, wherein the IR-absorbing organic pigment is selected from the group consisting of metal dithiolene complexes of formula (I), wherein M is Ni, Pd or Pt, X1, X2, independently of each other, are O or S, R1, R2, R3, R4 are the same or different and are selected from the group consisting of alkyl, wherein one or more non-adjacent alkyl CH2 radicals may be replaced by O, alkenyl, aryl and hetharyl, wherein aryl and hetharyl are unsubstituted or substituted, and naphthalocyanine complexes of formula (II) wherein M1 is Cu, Fe, Mn, Pd, Pt, VO, Si(OR8)2, Al(R7) or Ga(R7), R5 is H, F, OR9, SR9, NHR10, NR10R11, R6 is H, F, OR9, SR9, NHR10, NR10R11, R7 is selected from the group consisting of Cl, OH and OR12; R8 is selected from the group consisting of C1-C12 alkyl, (C2H4O)m-R13 and phenyl; R9 is selected from the group consisting of C1-C12 alkyl, (C2H4O)m-R13 and phenyl;R10, R11 independently of each other, are selected from the group consisting of C1-C12 alkyl, (C2H4O)n-R13 and phenyl or R10, R11 together form a saturated 5- or 6-membered N-heterocyclic ring, which is optionally substituted with 1 or 2 methyl groups; R12 is selected from the group consisting of C1-C12 alkyl, (C2H4O)n-R13 and phenyl; R13 is C1-C12 alkyl, and n, m independently of each other, are 0, 1, 2, 3 or 4.

5. The composition according to any of the preceding claims, comprising at least one dispersant selected from the group consisting of non-ionic or anionic polymeric dispersant having a plurality of C2-C4 poly(oxyalkylene) groups, acid polyethersters carrying at least one C2-C4 poly(oxyalkylene) group, or mixtures thereof with C2-C4 poly(oxyalkylene) glycols and / or anionic surfactants, and mixtures of polyamines modified with anionic surfactants carrying at least one C2-C4 poly(oxyalkylene) group.

6. The composition according to any of the preceding claims, which is an aqueous suspension of the microparticles.

7. The composition according to any of claims 1 to 5, which is a solid composition of the microparticles.

8. A method for producing the microparticle-based pigment composition according to any of the preceding claims comprising the following steps: i) providing an aqueous suspension of the IR-absorbing solid organic pigment particles also containing an aminoplastic precondensate of one or more amino compounds and one or more aldehydes; ii) effecting the polycondensation of the aminoplastic precondensate in the aqueous suspension of the IR-absorbing solid organic pigment in the presence of at least one surfactant.

9. The method according to claim 8, wherein the IR-absorbing solid organic pigment particles in the aqueous suspension are characterized by a volume-based particle size distribution, determined by static light scattering according to ISO 13320: 2009 EN, having a volume mean particle diameter D(v 0.5) of 0.8 pm at most.

10. The method according to any of claims 8 or 9, wherein the weight ratio of the surfactant to the IR-absorbing solid organic pigment is in the range of 0.05:1 to 1:

1.

11. The method according to any of claims 8 to 10, wherein the aqueous suspension of the solid IR-absorbing organic pigment is subjected to deagglomeration prior to step ii).

12. The use of a microparticle composition according to any of claims 1 to 7 for the preparation of a printing ink formulation, for security printing.

13. A printing ink formulation, in particular for security printing, containing a microparticle-based pigment composition according to any of claims 1 to 7 and a binder.

14. The printing ink formulation according to claim 13, wherein the binder comprises at least one oxidative drying resin.

15. A method for producing a security feature or a security document, comprising applying the printing ink formulation according to claim 13 or 14 to a substrate by means of a printing process, in particular by means of a printing process selected from the group consisting of copperplate intaglio printing, offset printing, gravure printing (also known as rotogravure), screen printing, flexography and combinations thereof, preferably by copperplate intaglio printing, offset printing or screen printing, more preferably by copperplate intaglio printing.

16. A security document comprising a substrate, on which a printing ink formulation according to any of claims 13 or 14 has been applied by a printing process.