RU2808573C2 - Composition of microparticles containing organic ir radiation absorbing pigment - Google Patents

Abstract

FIELD: microparticles.

SUBSTANCE: group of inventions relates to a microparticle-based pigment composition of an organic IR-absorbing pigment, which is a polyunsaturated organic compound or an organometallic compound having a main absorption maximum in the range from 750 to 1,100 nm, where the microparticles of the pigment composition contain an organic IR-absorbing pigment in the form of solid particles surrounded by or included 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 particle size distribution by volume, as determined by static light scattering, having an average by volume D value (4.3) in the range from 1.0 to 15.0 μm, where the amount of aminoplastic polymer in the microparticle composition is from 15 to 50 wt.%, based on the total mass of aminoplastic polymer and organic IR-absorbing pigment and wherein the amount of the organic IR-absorbing pigment is from 50 to 85% by weight based on the total weight of the aminoplastic polymer and the organic IR-absorbing pigment, wherein the aminoplastic polymer is a melamine-formaldehyde resin, also refers to a method for producing a microparticle-based pigment composition which includes the following steps: i) providing an aqueous suspension of solid organic IR-absorbing pigment particles that also contain an amino-based precondensate of one or more amino compounds and one or more aldehydes; ii) carrying out the polycondensation of an aminoplast-based precondensate in an aqueous suspension of a solid organic IR-absorbing pigment in the presence of at least one surfactant, also relates to the use of a microparticle composition to obtain a printing ink composition for security printing, also relates to a printing ink composition containing a microparticle-based pigment composition and a binder also relates to a method of producing a security feature or a security document that includes applying a printing ink composition to a substrate through a printing process, and refers to a security document containing a substrate onto which the printing ink composition has been applied through printing process.

EFFECT: group of inventions provides microparticles having both good absorption in the lower infrared region (NIR) and provides good stability against degradation in printing inks, and also provides microparticles containing IR absorbing pigment that can be used in small quantities compared to pigments from the prior art and through which also good stability of the IR absorbing pigment contained therein is achieved.

17 cl, 1 dwg, 1 tbl, 13 ex

Description

The present invention relates to microparticle compositions containing an organic IR absorbing pigment having a primary absorption maximum in the range from 750 to 1100 nm. The present invention also relates to a method for preparing said microparticle compositions and to their use in printing inks, in particular in printing inks that are suitable for producing a security feature or a security document.

BACKGROUND OF THE INVENTION

Colorless or barely colored IR absorbers satisfy a significant technical need in a wide range of applications such as security printing (banknotes, credit cards, ID cards, passports, etc.), invisible and/or IR-readable bar codes, laser welding of plastics, curing of surface coatings using infrared emitters, drying and curing of prints, curing of toner on paper or plastic, optical filters for PDP (plasma display panels), laser marking of e.g. paper or plastic, heating of plastic preforms or thermal protection applications.

A large number of organic and inorganic substances belonging to different classes of compounds and with a wide variety of different structures are known for use as IR absorbers (see, for example, EP 30672216 and references cited therein). Despite the large number of known classes and structures of compounds, obtaining products with complex property profiles is often difficult. There is an ongoing need for “colorless” IR absorbers, meaning that they have the lowest possible intrinsic color, while simultaneously meeting technical stability requirements such as chemical stability, thermal stability and/or light fastness.

Unfortunately, the chemical stability of IR-absorbing pigments is often unsatisfactory. In particular, IR absorbing pigments having a major absorption maximum in the range of 750 to 1100 and being colorless may be unstable, particularly with respect to oxidative stress. Therefore, there is still a need for high-tech applications of IR absorbing compounds to improve their oxidation resistance properties. This property is especially important for security printing applications. In the field of security printing, it is extremely important that the IR absorption properties remain high after the drying/curing step of the printing ink, and that the IR spectrum remains substantially unchanged from its original form before the drying/curing step. It is also important that a security element made from printed ink does not undergo a significant change in its absorption characteristics over the life of the security document. Finally, it is important that the IR-absorbing pigment contained in the printing ink does not degrade before the ink is actually used (shelf stability).

WO 2017/080652 describes security pigments in the form of core-shell particles that have a core made of a thermoplastic polymer containing a UV, visible or infrared dye, and a shell formed of a condensation polymer such as melamine-formaldehyde resin. The preparation involves preparing dye-containing polymer particles, followed by incorporating the thus obtained polymer particles into a duroplastic matrix, grinding the thus obtained matrix, and encapsulating the thus obtained dye-containing polymer particles with a condensation polymer. The resulting core-shell particles contain only a small amount of dye. Moreover, this concept is only applicable to those dyes that are soluble in organic solvents and compatible with the thermoplastic polymer.

WO 2017/080656 describes protective pigments in the form of core-shell particles that have a cross-linked duroplastic additive polymer core containing a UV, visible or IR dye and a shell formed by an additive polymer such as melamine-formaldehyde resin. Obtaining these pigments is labor-intensive. This requires preparing dye-containing polymer particles by incorporating the dye into a duroplastic matrix, grinding the matrix thus obtained, and encapsulating the thus obtained dye-containing polymer particles with a condensation polymer. The resulting core-shell particles should contain only a small amount of dye. Moreover, this concept is applicable only to those dyes that can be included in a duroplastic polymer matrix.

EP 30672216 describes pigment compositions containing an IR absorber and a stabilizing agent selected from thioamide, thiourea and thiocarbamate compounds such as trithiocyanuric acid, diphenylthiourea, dibutylthiourea, diisopropylthiourea, 2-mercapto-1-methylimidazole, 2-mercaptobenzyme idazole, N- phenylthioacetamide and their tautomers such as 2-thiomercaptopyrimidine compounds. Although these compositions provide improved stability of IR-absorbing pigments to both chemicals and light and do not impart coloration, low molecular weight stabilizing compounds may not always be acceptable, and long-term stability may not always be satisfactory since the stabilizers themselves may degrade.

Accordingly, there is a need for organic IR-absorbing pigment compositions that can be readily prepared from conventional IR-absorbing pigments, in particular organic IR-absorbing pigments, that provide increased stability of IR-absorbing pigments, in particular increased resistance against oxidative stress that occurs during oxidative drying of printing inks. In addition, the pigment composition must be compatible with printing inks and be capable of being easily incorporated into printing inks, in particular oxidatively drying printing inks.

Summary of the present invention

Surprisingly, it has been found that microparticle-based organic IR-absorbing pigment compositions as described herein satisfy technical stability requirements, in particular chemical stability, and can be easily incorporated into printing inks.

Therefore, the present invention relates to microparticle-based pigment compositions containing an organic IR-absorbing pigment having a major absorption maximum in the range from 750 to 1100 nm, wherein the microparticle pigment composition contains an organic IR-absorbing pigment in the form of solid particles that are surrounded by aminoplastic polymer or included in an aminoplastic polymer, which is a polycondensation product of one or more amino compounds and one or more aldehydes, wherein microparticle-based pigment compositions are characterized by a particle size distribution by volume, as determined by static light scattering according to ISO 13320:2009 EN, having a D value (4.3) in the range from 1.0 to 15.0 μm, in particular in the range from 3.0 to 12.0 μm.

The present invention also relates to a method for producing a microparticle-based pigment composition according to the present invention, which includes the following steps:

i) providing an aqueous suspension of a solid organic IR absorbing pigment that also contains an amino precondensate of one or more amino compounds and one or more aldehydes;

ii) carrying out polycondensation of the aminoplast-based precondensate in an aqueous suspension of a solid organic IR-absorbing pigment in the presence of at least one surfactant.

The present invention also relates to the use of a microparticle-based pigment composition in printing inks, in particular in oxidatively drying printing inks, in particular in printing inks that are suitable for intaglio printing.

According to another aspect, the present invention relates to printing inks, in particular, to printing inks for security printing, containing a microparticle-based composition as described herein, and a binder, in particular an oxidatively drying binder.

According to another aspect, the present invention relates to a method for producing a security feature or a security document, which includes applying a printing ink according to the present invention to a substrate through a printing process.

The present invention has a number of advantages. The microparticulate composition of the present invention provides increased stability of the IR absorbing pigments it contains, in particular resistance to chemicals and light. In particular, the compositions provide increased resistance to oxidative stress that occurs in oxidatively drying printing inks. Therefore, the IR absorption properties remain high after the drying/curing step of the printing ink and the IR spectrum remains essentially unchanged compared to its original form before the drying/curing step. Moreover, the compositions according to the present invention have good long-term stability and do not require the use of additional stabilizers. In addition, the compositions can be easily incorporated into printing inks. The method according to the present invention allows for the inclusion in the composition of high quantities of an organic pigment that absorbs infrared radiation. Thus, compositions can be prepared containing high amounts of organic IR absorbing pigment and relatively low amounts of other ingredients that may affect the pigment's IR absorption or other properties. Rather, the microparticle composition of the present invention has an IR absorption profile that is substantially unaffected by its aminoplast shell compared to the original untreated organic pigment.

Detailed Description of the Present Invention

As used herein and throughout the specification, the term “microparticulate composition” refers to compositions of discrete microparticles. The term "microparticle" indicates that discrete particles are typically of a size that does not exceed a few micrometers or even smaller, such as in the nanometer range. In particular, the term "microparticle" means at least 90 vol. %, based on the total volume of particles contained in the composition, particles having a size of less than 25 μm, in particular at most 20.0 μm, more particularly at most 17.5 μm and especially at most 15.0 μm, given as the D value (v 0.9).

Particle size as defined herein, as well as a particle size distribution characterized by, for example, D (v 0.1), D (v 0.5), D (v 0.9), D (3.2 ) and D(4,3), represents the diameter of particles, such as pigment particles and pigment-polymer particles, which can be determined by methods such as laser diffraction, which is also called static light scattering (SLS). SLS was performed in accordance with ISO 13320:2009 EN.

In the context of particle size, a value of D(0.9) or D(v 0.9) indicates that 90 vol. % of particles have a hydrodynamic diameter less than this value. In the context of particle size, the value of the volume-average particle diameter D (0.5) or D (v 0.5), respectively, means that 50 vol. % of particles have a diameter that exceeds the specified value, and 50 vol. % of particles have a diameter below the specified value. In the context of particle size, the value of D(0.1) or D(v 0.1) indicates that 10 vol. % of particles have a hydrodynamic diameter below the specified value. D(3,2) describes the surface weighted average of all particles, while D(4,3) describes the volume weighted average of all particles.

The microparticles contained in the microparticle composition contain an organic IR-absorbing pigment and an aminoplastic polymer. The organic IR absorbing pigment is incorporated into 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. In this regard, useful amino compounds are amines having at least two amino groups, in particular 2 or 3 amino groups. These amines are advantageously characterized in that each of their amino groups is attached to a carbon atom which is double bonded to an oxygen atom, a sulfur atom or a nitrogen atom. Preferred examples of such amines are urea, thiourea and melamine, cyanoguanamine (=dicyandiamide), acetoguanamine and benzoguanamine. Suitable aldehydes in this regard are C ₁ -C ₁₀ alkanals, especially C ₁ -C ₄ alkanes such as formaldehyde, acetaldehyde, propanal or n-butanal, and C ₂ -C ₁₀ alkanedials, especially C ₂ -C ₆ -alkanedials such as glyoxal or glutaraldehyde. Preferred aldehydes are formaldehyde, glyoxal and glutaraldehyde, in particular formaldehyde. The aminoplastic polymer may be partially or fully esterified.

The aminoplastic polymer of the microparticle composition according to the present invention is typically selected from melamine-formaldehyde resins (= MF resins), including fully or partially esterified MF resins, urea-formaldehyde resins (= UF resins), thiourea-formaldehyde resins (= TUF resins), melamine-urea-formaldehyde resins (= MUF resins), including fully or partially esterified MUF resins, melamine-thiourea-formaldehyde resins (= MTUF resins), including partially esterified MTUF resins, urea-glutaraldehyde resins, benzoguanamine-formaldehyde resins, dicyandiamide-formaldehyde resins and urea-glyoxal resins, i.e. from polymers obtained by the polycondensation of mixtures of melamine, urea, thiourea, mixtures of melamine/(thio)urea, benzoguanamine or dicyandiamide with formaldehyde, the polycondensation of urea with glutaraldehyde or the polycondensation of urea with glyoxal.

The aminoplastic polymer of the microparticle composition according to the present invention is preferably selected from MF resins, including fully or partially esterified MF resins, and melamine urea formaldehyde resins (=MUF resins), including fully or partially esterified MUF resins, in particular MF resins, and especially fully or partially esterified MF resins

The amount of aminoplastic polymer in the microparticle composition of the present invention is generally from 15 to 50 wt. %, in particular from 17 to 45 wt. % and especially from 19 to 42 wt. %, based on the total weight of the aminoplastic polymer and organic IR-absorbing pigment. Therefore, the amount of IR-absorbing pigment in the microparticle composition of the present invention is generally from 50 to 85 wt. %, in particular from 55 to 83 wt. % and especially from 68 to 81 wt. %, based on the total weight of the aminoplastic polymer and organic IR-absorbing pigment.

In principle, any IR-absorbing organic compound known in the art that has a major absorption maximum in the range of 750 to 1100 nm is suitable for use as an organic IR-absorbing pigment contained in the microparticulate composition of the present invention. invention. Preference is given to IR-absorbing pigments that are “colorless,” meaning that they have minimal absorption in the visible range of the electromagnetic spectrum, particularly between 400 and 700 nm.

Pigments in the context of the present invention are polyunsaturated polycyclic organic compounds or organometallic compounds that have a major absorption maximum in the range from 750 to 1100 nm. Particular preference is given to polycyclic organic organometallic compounds, in particular complexes of mono- or polyunsaturated mono- or polycyclic organic compounds with a metal or semi-metal, where the mono- or polyunsaturated mono- or polycyclic organic compound together with a metal atom or semi-metal forms a polyunsaturated polycyclic organometallic compound. The pigments of the present invention are mainly composed of polyunsaturated polycyclic organic compounds or organometallic compounds. The organic pigments according to the present invention in particular contain less than 60 wt. %, in particular less than 50 wt. % or less than 40 wt. %, or even less than 30 wt. %, based on the total mass of pigment, an organic substance that does not have a main absorption maximum in the range from 750 to 1100 nm.

Often the organic IR absorbing pigment is selected from the group consisting of dithiolene metal complexes, phthalocyanine pigments, naphthalocyanine pigments, rylene pigments, polymethine pigments and anthraquinone pigments, in particular the pigments detailed in EP 3067216, which is incorporated herein by reference, as well as mixtures of these pigments.

More preferably, the organic IR absorbing pigment of the microparticle composition of the present invention is selected from naphthalocyanine pigments and dithiolene metal complexes. Suitable naphthalocyanine pigments are the compounds of formulas IIIc, IIId and IIIe disclosed in EP 3067216, which is incorporated herein by reference. Suitable dithiolene metal complexes are those described for example by formulas IIa and IIb in EP 3067216, and in particular those described by formula (I) in WO 2008/086931 or formula (I) in WO 2012/069518, which are incorporated herein by links.

According to a specific embodiment of the present invention, the organic IR absorbing pigment of the microparticle composition of the present invention is selected from the group consisting of dithiolene metal complexes of formula (I),

Where

M represents Ni, Pd or Pt,

X ¹ , X ² , independently of each other, represent O or S,

R ¹ , R ² , R ³ and R ⁴ are the same or different and are selected from the group consisting of alkyl, where one or more non-adjacent CH ₂ alkyl radicals may be substituted by O, alkenyl, aryl and hetaryl, where aryl and hetaryl are unsubstituted or substituted.

As used herein and throughout the specification, the term “alkyl” refers to a linear or branched saturated hydrocarbon radical having generally from 1 to 18 carbon atoms, in particular from 1 to 12 carbon atoms, often from 1 to 6 carbon atoms, in in particular from 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, n-hexyl, 2-hexyl, 2,3-dimethylbutyl, n-heptyl, 2-heptyl, n-octyl, 2-octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, n-nonyl, 2-nonyl, n-decyl, 2-decyl, n-undecyl, 2-undecyl, n-dodecyl, 2-dodecyl and 2,4,4,6,6-pentamethyldecyl.

As used herein and throughout the specification, the term "alkyl, wherein one or more non-contiguous CH ₂ alkyl radicals are substituted with O" refers to a linear or branched, saturated aliphatic radical having generally from 3 to 18 carbon atoms, in particular from 4 to 12 carbon atoms where at least 1 of the CH ₂ groups, for example 1, 2, 3 or 4 non-adjacent CH ₂ groups, is replaced by O, thereby 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)-ethoxy)ethyl, 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.

As used herein and throughout the specification, the term “alkenyl” refers to a linear or branched, unsaturated hydrocarbon radical having typically 2 to 18 carbon atoms, in particular 3 to 12 carbon atoms, often 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; C ₂ -C ₆ -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, 1-methyl-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-propenyl, 1-ethyl-1-propenyl, 1-ethyl-2- propenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl, 1-methyl-1-pentenyl, 2-methyl-1-pentenyl, 3-methyl-1-pentenyl, 4-methyl- 1-pentenyl, 1-methyl-2-pentenyl, 2-methyl-2-pentenyl, 3-methyl-2-pentenyl, 4-methyl-2-pentenyl, 1-methyl-3-pentenyl, 2-methyl-3- pentenyl, 3-methyl-3-pentenyl, 4-methyl-3-pentenyl, 1-methyl-4-pentenyl, 2-methyl-4-pentenyl, 3-methyl-4-pentenyl, 4-methyl-4-pentenyl, 1,1-dimethyl-2-butenyl, 1,1-dimethyl-3-butenyl, 1,2-dimethyl-1-butenyl, 1,2-dimethyl-2-butenyl, 1,2-dimethyl-3-butenyl, 1,3-dimethyl-1-butenyl, 1,3-dimethyl-2-butenyl, 1,3-dimethyl-3-butenyl, 2,2-dimethyl-3-butenyl, 2,3-dimethyl-1-butenyl, 2,3-dimethyl-2-butenyl, 2,3-dimethyl-3-butenyl, 3,3-dimethyl-1-butenyl, 3,3-dimethyl-2-butenyl, 1-ethyl-1-butenyl, 1- ethyl-2-butenyl, 1-ethyl-3-butenyl, 2-ethyl-1-butenyl, 2-ethyl-2-butenyl, 2-ethyl-3-butenyl, 1,1,2-trimethyl-2-propenyl, 1-ethyl-1-methyl-2-propenyl, 1-ethyl-2-methyl-1-propenyl, 1-ethyl-2-methyl-2-propenyl and the like, or C ₂ -C ₈ -alkenyl, such as radicals mentioned for C ₂ -C ₆ -alkenyl and additionally 1-heptenyl, 2-heptenyl, 3-heptenyl, 1-octenyl, 2-octenyl, 3-octenyl, 4-octenyl and their positional isomers.

As used herein and throughout the specification, the term “aryl” refers to mono- or polycyclic aryl, while the term “hetaryl” refers to mono- or polycyclic hetaryl, where the terms “monocyclic aryl”, “polycyclic aryl”, “monocyclic hetaryl” and "polycyclic aryl" are as defined herein.

As used herein and throughout the specification, the term “substituted” in the context of aryl and hetaryl means that the 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 R ^a radicals, as defined below.

As used herein and throughout the specification, the terms “monocyclic aromatic radical” and “monocyclic aryl” refer to phenyl.

As used herein and throughout this specification, the term “polycyclic aryl” refers to:

(i) a polycyclic aromatic hydrocarbon radical, i.e. a completely unsaturated polycyclic hydrocarbon radical, where each of the carbon atoms is part of a conjugated π-electron system,

(ii) a polycyclic hydrocarbon radical containing one phenyl ring fused to a saturated or unsaturated 4-10 membered mono- or bicyclic hydrocarbon ring,

(iii) a polycyclic hydrocarbon radical which bears at least 2 phenyl rings which are directly fused to each other and/or which are fused to a saturated or unsaturated 4-10 membered mono- or bicyclic hydrocarbon ring.

Typically, 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 carbon, especially 10, 12, 13, 14 or 16 carbon atoms.

In this context, polycyclic aryl bearing 2, 3 or 4 phenyl rings that are directly fused to each other includes, for example, naphthyl, anthracenyl, phenanthrenyl, pyrenyl and triphenylenyl. Polycyclic aryl bearing 2, 3 or 4 phenyl rings, which are fused with a saturated or unsaturated 4-10 membered mono- or bicyclic hydrocarbon radical, include, for example, 9H-fluorenyl, biphenylenyl, tetraphenylenyl, acenaphthenyl(1,2-dihydroacenaphthenyl ), acenaphthenyl, 9,10-dihydroanthracen-1-yl, 1,2,3,4-tetrahydrophenanthrenyl, 5,6,7,8-tetrahydrophenanthrenyl, cyclopent[fg]acenaphthenyl, phenalenyl, fluoranthenyl, benzo[k]fluoranthenyl, perylenyl, 9,10-dihydro-9,10[1',2']-benzenoanthracenyl, dibenzo[a,e][8]annulenyl, 9,9'-spirobi[9H-fluoren]yl and spiro[1H-cyclobuta [de]naphthalene-1,9'-[9H]fluoren]yl.

Polycyclic aryl includes by way of example naphthyl, 9H-fluorenyl, phenanthrenyl, anthracenyl, pyrenyl, acenaphthenyl, acenaphthenyl, 2,3-dihydro-1H-indenyl, 5,6,7,8-tetrahydro-naphthalenyl, cyclopent[fg]acenaphthenyl, 2,3-dihydrophenanthrenyl, 9,10-dihydroanthracen-1-yl, 1,2,3,4-tetrahydrophenanthrenyl, 5,6,7,8-tetrahydrophenanthrenyl, fluoranthenyl, benzo[k]fluoranthenyl, biphenylenyl, triphenylenyl, tetraphenylenyl, 1,2-dihydroacenaphthenyl, dibenzo[a,e][8]annulenyl, perylenyl, biphenylyl, tetraphenylyl, naphthylenephenyl, phenanthrenylphenyl, anthracenyl phenyl, pyrenylphenyl, 9H-fluorenylphenyl, di(naphthylene)phenyl, naphthylenebiphenyl, tri(phenyl)phenyl, tetra(phenyl)phenyl, pentaphenyl(phenyl), phenylnaphthyl, binaphthyl, phenanthrenylnaphthyl, pyrenylnaphthyl, phenylanthracenyl, biphenylanthracenyl, naphthalenylanthracenyl, phenanthrenylanthracenyl, dibenzo[a,e][8]annulenyl, 9,10-dihydro-9,10[1' ,2']benzoanthracenyl, 9,9'-spirobi-9H-fluorenyl and spiro[1H-cyclobuta[de]naphthalene-1,9'-[9H]fluoren]yl.

As used herein and throughout the specification, the terms “monocyclic heteroaromatic radical” and “monocyclic hetaryl” refer to a heteroaromatic monocyclic radical in which the ring member atoms are part of a conjugated π electron system, where the heteroaromatic monocycle has 5 or 6 ring atoms that contain as members of a heterocyclic ring, 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 remaining ring atoms are carbon atoms. Examples include furyl (= furanyl), pyrrolyl (= 1H-pyrrolyl), thienyl (= thiophenyl), imidazolyl (= 1H-imidazolyl), pyrazolyl (= 1H-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.

As used herein and throughout the specification, the term “polycyclic hetaryl” refers to a heteroaromatic polycyclic radical that bears a monocyclic hetaryl ring as defined above and at least one, for example 1, 2, 3, 4 or 5, additional aromatic rings selected of phenyl and heteroaromatic monocycles as defined above, wherein the aromatic rings of the polycyclic hetaryl are covalently bonded to each other and/or fused to each other directly and/or fused to a saturated or unsaturated 4-10 membered mono- or bicyclic hydrocarbon ring. The term "polycyclic hetaryl" also refers to heteroaromatic polycyclic radicals that bear at least one saturated or partially unsaturated 5- or 6-membered heterocyclic ring bearing 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, where at least one of the additional aromatic rings is directly fused with a saturated or partially unsaturated 5- or 6-membered heterocyclic radical, and where the remaining aromatic rings polycyclic hetaryl are linked to each other by a covalent bond or fused to each other directly and/or fused to a saturated or unsaturated 4-10 membered mono- or bicyclic hydrocarbon ring. Typically, polycyclic hetaryl has from 9 to 26 ring atoms, in particular from 9 to 20 ring atoms, which include 1, 2, 3 or 4 atoms selected from nitrogen atoms, sulfur atoms and oxygen atoms, where the remaining ring atoms are carbon atoms .

Examples of polycyclic heteroaryl include, but are not limited to, benzofuryl, benzothienyl, dibenzofuranyl (=dibenzo[b,d]furanyl), dibenzothienyl (=dibenzo[b,d]thienyl), naphthofuryl, naphthothienyl, furo[3,2-b]furanyl, furo[ 2,3-b]furanyl, furo[3,4-b]furanyl, thieno[3,2-b]thienyl, thieno[2,3-b]thienyl, thieno[3,4-b]thienyl, oxanthrenyl, thianthrenyl, indolyl (= 1H-indolyl), isoindolyl (= 2H-isoindolyl), carbazolyl, indolizinyl, benzopyrazolyl, benzimidazolyl, benzoxazolyl, benzothiazolyl, benzo[cd]indolyl, 1H-benzo[g]indolyl, quinolinyl, isoquinolinyl, acridinyl, phenazinyl, quinazolinyl, quinoxalinyl, phenoxazinyl, fenthiazinyl, benzo[b][1,5]naphthyridinyl, cinnolinyl, 1,5-naphthyridinyl, 1,8-naphthyridinyl, phenylpyrrolyl, naphthyl pyrrolyl, dipyridyl, phenylpyridyl, naphthylpyridyl, pyrido [ 4,3-b]indolyl, pyrido[3,2-b]indolyl, pyrido[3,2-g]quinolinyl, pyrido[2,3-b][1,8]naphthyridinyl, pyrrolo[3,2- b]pyridinyl, pteridinyl, puryl, 9H-xanthenyl, 9H-thioxanthenyl, 2H-chromenyl, 2H-thiochromenyl, phenanthridinyl, phenanthrolinyl, furo[3,2-f][1]benzofuranyl, furo[2,3-f][ 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]quinolinyl, thieno[2,3-g]quinolinyl, thieno[2,3-g]quinoxalinyl, benzo[g] tichochromenyl, pyrrolo[3,2,1-hi]indolyl, benzo[g]quinoxalinyl, benzo[f]quinoxalinyl and benzo[h]isoquinolinyl.

As used herein and throughout the specification, the term “cycloalkyl” refers to a mono- or polycyclic saturated hydrocarbon radical having typically 3 to 12 carbon atoms, often 3 to 8 carbon atoms, in particular 5 to 6 carbon atoms , such as cyclopentyl, cyclohexyl, norbornyl or admantyl.

The metal atom M in the dithiolene complex of formula (I) is preferably nickel or platinum and is in particular nickel.

The variables X ¹ and X ² in formula (I) may be different, but are preferably identical and both represent either sulfur or oxygen.

In a particularly preferred embodiment, X ¹ and X ² are both sulfur.

Preferably, the radicals R ¹ , R ² , R ³ and R ⁴ are independently selected from C ₁ -C ₈ alkyl, phenyl, polycyclic aryl, such as especially naphthyl, mono- and polycyclic hetaryl, such as especially pyridyl, furyl, thienyl, imidazolyl or pyrazolyl, wherein phenyl, polycyclic aryl, mono- and polycyclic hetaryl may be unsubstituted or substituted by 1, 2, 3, 4 or 5 R ^a radicals.

The radicals R ^a are independently selected from the group consisting of halogen, C ₁ -C ₈ -alkyl, C ₁ -C ₈ -haloalkyl, C ₁ -C ₈ -alkoxy, C ₁ -C ₈ -alkylthio , C ₃ -C ₈ -cycloalkyl, heterocycloalkyl, aryl, hetaryl, hydroxyl, mercapto, cyano, nitro, COOH, SO ₃ H and NE ¹ E ² , where E ¹ and E ² in each case independently represent hydrogen , C ₁ -C ₆ -alkyl, C ₃ -C ₈ -cycloalkyl, heterocycloalkyl, aryl or hetaryl. In particular, the R ^a radicals are independently selected from the group consisting of fluorine, chlorine, bromine, cyano, nitro, C ₁ -C ₄ -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl or tert-butyl, C ₁ -C ₄ -haloalkyl, such as fluoromethyl, difluoromethyl, trifluoromethyl, chloromethyl, dichloromethyl 2-fluoroethyl, 2,2-difluoroethyl or 2,2,2-trifluoroethyl, C ₁ - C ₃ -alkoxy such as methoxy, ethoxy, n-propoxy or isopropoxy, C ₃ -C ₆ -cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl, aryl such as phenyl or naphthyl, and hetaryl 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 in particular from methyl, ethyl, isopropyl, fluorine and trifluoromethyl.

In particular, the radicals R ¹ , R ² , R ³ and R ⁴ are independently of each other C ₁ -C ₈ alkyl or aryl, where aryl is either substituted by one or two ^Ra radicals, which have the meanings defined herein, particularly preferred, or is unsubstituted, i.e. does not carry any R ^a radicals. In the case where the radicals R ¹ , R ² , R ³ and/or R ⁴ are replaced by two radicals R ^a , the two radicals R ^a are preferably identical.

Particularly preferably, the radicals R ¹ , R ² , R ³ and R ⁴ are independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, n-hexyl, n-octyl, 2- ethylhexan-1-yl, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-ethylphenyl, 3-ethylphenyl, 4-ethylphenyl, 2-isopropylphenyl, 3-isopropylphenyl, 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- methyl phenyl trifluoro, 3,5-di-trifluoromethyl-phenyl, 2-6-di-trifluoromethyl-phenyl, naphth-1-yl, naphth-2-yl, pyridin-2-yl, pyridin-3-yl, pyridine -4-yl, fuarn-2-yl, furan-3-yl, thien-2-yl and thien-3-yl.

Particularly preferred are dithiolene metal complexes of formula (I), wherein the radicals R ¹ , R ² , R ³ and R ⁴ all have the same meaning, which is selected from the meanings defined herein, in particular the preferred meanings.

According to another specific embodiment of the present invention, the organic IR absorbing pigment contained in the microparticulate composition of the present invention is selected from the group consisting of naphthal oyl cyanine complexes of formula (II),

Where

M ¹ represents Cu, Fe, Mn, Pd, Pt, VO, Si(OR ⁸ )2, Al(R ⁷ ) or Ga(R ⁷ ),

R ⁵ represents H, F, OR ⁹ , SR ⁹ , NHR ¹⁰ , NR ¹⁰ R ¹¹ ,

R ⁶ represents H, F, OR ⁹ , SR ⁹ , NHR ¹⁰ , NR ¹⁰ R ¹¹ ,

R' is selected from the group consisting of Cl, OH and OR ¹² ;

R ⁸ is selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _m -R ¹³ and phenyl;

R ⁹ is selected from the group consisting of C1-C ₁₂ alkyl, (C ₂ H ₄ O) _m -R ¹³ and phenyl;

R ¹⁰ , R ¹¹ are independently selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _n -R ¹³ and phenyl, or

R ¹⁰ , R ¹¹ together form a 5- or 6-membered saturated N-heterocyclic ring, which is optionally substituted with 1 or 2 methyl groups;

R ¹² is selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _n -R ¹³ and phenyl;

R ¹³ represents C ₁ -C ₁₂ -alkyl, and

n, m independently represent 0, 1, 2, 3 or 4.

The M ¹ fragment in the naphthaloyl cyanine complex of formula (II) is preferably selected from the group consisting of Cu, Ga, Fe, Mn, Pd and Pt, in particular Cu, Ga and Fe.

Preferably, the radicals R ⁵ and R ⁶ in formula (II) are independently selected from the group consisting of H, F, OR ⁹ and NHR ¹⁰ , in particular H, F and OR ⁹ .

According to a preferred embodiment of the present invention, the radicals R ⁵ and R ⁶ have the same meaning.

The radicals R ⁷ , R ⁸ , R ⁹ , R ¹⁰ , R ¹⁰ , R ¹⁰ , R ¹⁰ , n and m have the following preferred meanings:

R ⁷ represents OH or OR ¹² , in particular OR ¹² ;

R ⁸ represents C ₁ -C ₈ -alkyl or (C ₂ H ₄ O) _m -R ¹³ , in particular C ₁ -C ₈ -alkyl;

R ⁹ represents C ₁ -C ₈ -alkyl or (C ₂ H ₄ O) _m -R ¹³ , in particular (C ₂ H ₄ O) _m -R ¹³ ;

R ¹⁰ and R ¹¹ independently of each other represent C ₁ -C ₈ -alkyl or (C ₂ H ₄ O) _n -

R ¹³ , more preferably C ₁ -C ₆ -alkyl or (C ₂ H ₄ O) _n -R ¹³ , with n and R ¹³ having preferred meanings as defined herein, or

R ¹⁰ and R ¹¹ together form a 5- or 6-membered saturated N-heterocyclic ring;

R ¹² represents C ₁ -C ₈ -alkyl or (C ₂ H ₄ O) _n -R ¹³ ;

R ¹³ represents C ₁ -C ₈ -alkyl, in particular C ₁ -C ₆ -alkyl;

pit independently of each other 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 often in the range from 2.0 to 14.0 μm, in particular in the range from 3.0 to 12.0 μm, preferably in the range from 3.5 to 11.0 µm, more preferably in the range from 4.0 to 10.0 µm and especially in the range from 4.5 to 9.5 µm as determined by static light scattering.

In the microparticle composition according to the present invention, the D(v 0.5) of the microparticles is often in the range from 1.8 to 12.5 μm, in particular in the range from 2.8 to 11.0 μm, preferably in the range from 3.0 to 9.5 µm, more particularly in the range from 3.2 to 9.2 µm and especially in the range from 3.5 to 9.0 µm as determined by static light scattering.

In the microparticle composition according to the present invention, the surface-weighted average diameter D(3,2) of the microparticles is often in the range from 1.6 to 12.5 μm, in particular in the range from 2.6 to 10.5 μm, preferably in the range from 2.8 to 9.2 µm, more particularly in the range from 3.0 to 9.0 µm and especially in the range from 3.2 to 8.8 µm as determined by static light scattering.

In the microparticle composition according to the present invention, the particle diameter D(v 0.1) of the microparticles is often at least 1.0 μm, in particular at least 2.0 μm, more particularly at least 2.4 μm and especially at least 2.7 µm, for example in the range from 1.0 to 8.0 µm, in particular in the range from 2.0 to 7.0 µm, more particularly in the range from 2.4 to 6.0 µm, and especially in range from 2.7 to 5.5 µm, as determined by static light scattering.

In the microparticle composition according to the present invention, the particle diameter D(v 0.9) of the microparticles is often at most 20.0 μm, in particular at most 17.5 μm and especially at most 15.0 μm, for example in the range of 4.0 to 20.0 µm, in particular from 5.0 to 17.5 µm, more particularly in the range from 6.0 to 15.0 µm, as determined by static light scattering.

Often, the microparticulate composition of the present invention contains at least one dispersant, which may serve to stabilize the pigment particles against agglomeration during the preparation of the microparticulate composition of the present invention, but may also beneficially influence the properties of the microparticulate composition of the present invention , in particular with regard to their inclusion in printing inks.

Suitable dispersants are known to those skilled in the art. A general overview of the different types of polymer dispersants, their polymer structure and their properties is given in 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. Suitable polymeric dispersants in the context of the present invention are essentially organic polymers which are soluble or at least dispersible in water and which have at least one polar group which makes the polymer soluble or dispersible in water and often at least one anchor group , which is capable of adsorbing on the surface of a pigment particle. Anchoring can be achieved through hydrogen bonds, dipole-dipole interactions, pi-pi interactions, London or van der Waals forces, and a combination of these.

Preferably, the microparticulate composition of the present invention contains at least one selected dispersant having one or more poly(oxy-C ₂ -C ₄ -alkylene) groups. The polyoxyalkylene group imparts water solubility or dispersibility to the polymeric dispersant and serves to sterically stabilize the pigment particles against agglomeration in the aqueous phase. The molecular weight of polyoxyalkylene groups can vary from 200 to 5000 g/mol (number average), corresponding to a range of 3 to 110 oxyalkylene repeating units.

As used herein and throughout the specification, the terms "polyoxyalkylene group", "polyalkylene oxide group" and polyalkylene glycol group are used as synonyms and refer to oligomeric or polymeric groups or moieties that consist of repeating alkyleneoxy units, in particular C ₂ -C ₄ - alkylene oxide repeating units, i.e. repeating units of the formula A-O, where A is a C ₂ -C ₄ -alkanediyl, such as 1,2-ethanediyl, 1,2-propanediyl, 1,2-butanediyl, 2,3-butanediyl or 1-methyl-1 ,2-propanediyl, and especially from ethyleneoxy (CH ₂ CH ₂ O) and/or propyleneoxy (CH(CH ₃ )CH ₂ O) repeating units. Polyoxyalkylene groups consisting of C ₂ -C ₄ -alkylene oxide repeating units are hereinafter referred to as poly(oxy-C ₂ -C ₄ -alkylene) groups or poly-C ₂ -C ₄ -alkylene glycol groups, respectively. Polyoxyalkylene groups consisting of ethylene oxide and/or propylene oxide repeating units are hereinafter designated poly(oxy-C ₂ -C ₃ -alkylene) groups or poly-C ₂ -C ₃ -alkylene glycol groups, respectively. Polyoxyalkylene groups may be uncapped, for example they have a terminal OH group, or they may be capped, meaning that they carry a terminal O-linked hydrocarbon radical such as C ₁ -C ₁₂ -alkyl, C ₃ -C ₁₂ -alkyl or benzyl.

Suitable anchor 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 C ₁ -C ₂₂ -alkyl, C ₂ - C ₂₀ -alkenyl, OH, amino (NH ₂ ), aminosulfonyl (SO ₂ NH ₂ ) and carbamoyl (CONH ₂ );

- aryl radicals, such as phenyl or naphthyl, where the aryl carries at least one, for example 1, 2 or 3 radicals, which are selected from OH, amino (NH ₂ ), aminosulfonyl (SO ₂ NH ₂ ) and carbamoyl (CONH ₂ ), and optionally 1, 2 or 3 radicals, which are selected from C ₁ -C ₄ -alkyl;

- long-chain fatty acid radicals, often having from 8 to 22 carbon atoms, such as C ₈ -C ₂₂ -alkyl, C ₈ -C ₂₂ -alkenyl or C ₈ -C ₂₂ -alkanediyl;

- lactamyl groups, such as pyrrolidone, caprolactone or morpholinone groups; And

- urethane or urea groups, including imidazolide groups and triazinetrione groups.

In particular, the microparticulate compositions of the present invention contain at least one dispersant selected from the group consisting of

- nonionic or anionic polymeric dispersants having multiple poly(oxy-C ₂ -C ₄ -alkylene) groups (type I dispersant),

- acidic polyethers containing ester groups bearing at least one poly(oxy-C ₂ -C ₄ -alkylene) group, or mixtures thereof with poly(oxy-C ₂ -C ₄ -alkylene) glycols and/or anionic surface -active substances (type II dispersant), and

- mixtures of a fatty acid modified polyalkyleneimine and at least one anionic surfactant bearing at least one poly(oxy-C ₂ -C ₄ -alkylene) group (type III dispersant).

Examples of Type I dispersant include nonionic or anionic polymers having a polyurethane backbone wherein polyoxyalkylene groups form part of the backbone or side chains, and nonionic or anionic polymers having a carbon backbone wherein polyoxyalkylene groups are present as side chains.

Specific Group I type dispersants are selected from nonionic comb polymers and anionic comb polymers having a carbon backbone wherein polyoxyalkylene groups are present as side chains, and mixtures thereof.

In particular, the Type I polymer dispersant is selected from comb polymers containing both repeat units bearing poly-C ₂ -C ₄ -alkylene ether groups and repeat units from monomers having an anchor group, and mixtures thereof with comb polymers having both repeating units bearing poly-C ₂ -C ₄ -alkylene ether groups and repeating units from acid monomers. These comb polymers often consist of polymerized repeating units of ethylenically unsaturated monomers M containing in polymerized form at least one monoethylenically unsaturated monomer having an anchor group (M1 monomer) or an acid group (M1'), a monoethylenically unsaturated monomer bearing a poly(oxyalkylene) group, in particular a poly(oxy-C ₂ -C ₄ -alkylene) group and especially a poly(oxy-C ₂ -C ₃ -alkylene) group (monomer M2) and, optionally, a nonionic monomer M3 other than these. It will be apparent to one skilled in the art that these types of polymers can be prepared by polymerizing monomers M1, M2 and optionally M3, for example by radical polymerization, subjecting the polymer consisting of monomers M1 and M3 to a polymer-like reaction with the OH-terminal poly (oxy-C ₂ -C ₄ -alkylene) ether, in particular multifunctional OH-terminal poly(oxy-C ₂ -C ₄ -alkylene) ethers, especially multifunctional OH-terminal poly(oxy-C ₂ -C ₃ -alkylene ) ether, provided that the M3 monomers have a functional group that is capable of undergoing an esterification or trans-esterification reaction, for example, a carboxyl group or a C ₁ -C ₆ -alkoxycarbonyl group.

Suitable M1 monomers are

- N-vinyl lactams, such as N-vinylpyrrolidone, N-vinylcaprolactam and N-vinyl;

- vinyl- or allyl-substituted heterocycles, such as vinylpyridines, N-vinylimidazole, N-vinyltriazole and N-vinylpyrazole;

vinylpyridines are particularly preferred.

Suitable monomers M1' are monoethylenically unsaturated carboxylic acids, in particular monoethylenically unsaturated monocarboxylic acids with 3 to 6 carbon atoms, such as acrylic acid or methacrylic acid, and monoethylenically unsaturated dicarboxylic acids with 4 to 6 carbon atoms, such as maleic acid or itaconic acid acid.

Suitable M2 monomers are, for example,

- vinyl and allylic ethers of poly(oxy-C ₂ -C ₄ -alkylene) ethers, which are also terminated with poly-C ₂ -C ₄ -alkylene glycols and especially poly-C ₂ -C ₃ -alkylene glycols;

- esters of acrylic acid with poly(oxy-C ₂ -C ₄ -alkylene ethers), in particular with poly(oxy-C ₂ -C ₄ -alkylene ethers) and especially with poly(oxy-C _{2 -alkylene} ethers) -C ₃ -alkylene), and esters of methacrylic acid with poly(oxy-C ₂ -C ₄ -alkylene ethers), in particular with poly(oxy-C ₂ -C ₃ -alkylene ethers), which in the future also are called poly-C ₂ -C ₄ -alkylene glycol (meth)acrylate and poly-C ₂ -C ₃ -alkylene glycol (meth)acrylate, respectively

- diesters of maleic acid or fumaric acid with poly(oxy-C ₂ -C ₄ -alkylene ethers) and especially with poly(oxy-Cr-C ₃ -alkylene ethers).

In the above-mentioned M2 monomers, the poly(oxy-C ₂ -C ₄ -alkylene) group may be uncapped, i.e. ends with a hydroxy group, or capped, i.e. ends with a hydrocarbon radical connected to O, for example, a C ₁ -C ₈ -alkyloxy group. For example, the poly(oxyalkylene) group is a C ₁ -C ₆ alkyl-terminated polyoxyethylene group or a C ₁ -C ₆ -alkyl-terminated polyethylene glycol group, respectively, a methyl-terminated polyoxyethylene group or a methyl-terminated polyethylene glycol group, respectively .

The molecular weight of the poly(oxy-C ₂ -C ₄ -alkylene) glycol group in Type I dispersants can vary from 200 to 5000 g/mol, corresponding to 3 to 110 oxyalkylene repeating units.

Among the above M2 monomers, preference is given to esters of acrylic acid with poly(oxy-C ₂ -C ₄ -alkylene) ethers, in particular with poly(oxy-C ₂ -C ₃ -alkylene) ethers and esters of methacrylic acid with poly (oxyalkylene) ethers, in particular poly(oxy-C ₂ -C ₃ -alkylene) ethers. Particularly preferred are poly-C ₂ -C ₆ alkyl-terminated poly-C ₂ -C ₄ -alkylene glycol (meth)acrylates, in particular C ₁ -C ₆ alkyl-terminated poly-C ₂ -C ₃ -alkylene glycol (meth)acrylates and more particularly C ₁ -C ₆ alkyl-terminated polyethylene glycol (meth)acrylates, especially corresponding to methyl-terminated polyalkylene glycol (meth)acrylates.

Suitable M3 monomers are, for example,

- C ₁ -C ₈ alkyl vinyl ethers and C ₁ -C ₈ alkyl lyl ethers;

- vinyl esters and allyl esters of C ₁ -C ₈ alkanoic acids, such as vinyl acetate or vinyl propionate;

- esters of acrylic acid and esters of methacrylic acid with C1-C12 alkanols, esters of acrylic acid and esters of methacrylic acid with C5-C12 cycloalkanols, in particular esters of acrylic acid and esters of methacrylic acid with C1-C6 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;

- vinyl aromatic hydrocarbons such as styrene and vinyltoluene;

- diesters of maleic acid with C ₁ -C ₁₂ alkanols, such as dibutyl maleate and dibutifumarate.

Among the above M3 monomers, preferred are esters of acrylic acid with C ₁ -C ₁₂ -alkanols and esters of methacrylic acid with C ₁ -C ₁₂ -alkanols, hereinafter referred to as C ₁ -C ₁₂ -alkyl(meth)acrylates. Particularly preferred are esters of acrylic acid with C ₁ -C ₆ alkanols and esters of methacrylic acid with C ₁ -C ₆ alkanols, hereinafter referred to as C ₁ -C ₆ alkyl (meth)acrylates.

In particular, the Type I dispersant contains a non-ionic comb-shaped polymer containing carbon, where the carbon backbone has both repeat units bearing a poly(oxy-C ₂ -C ₄ -alkylene) group and repeat units derived from vinyl pyridine units, or its mixture with a comb-shaped polymer, where the carbon backbone has both repeating units bearing a poly(oxy-C ₂ -C ₄ -alkylene) group and repeating units derived from one or more MG monomers.

Type II dispersants contain at least one anionic polyester containing ester groups having one or more poly(oxy-C ₂ -C ₄ -alkylene) groups, which in particular is a polyester containing ester groups, poly (hydroxy-C ₂ -C ₄ -alkylene) glycol, in particular polyethylene glycol, with an ester of an aromatic dicarboxylic acid, such as phthalic acid or terephthalic acid, and a diol component that 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 poly(oxy-C ₂ -C ₄ -alkylene) glycol groups in the anionic polyester dispersants of type II can in particular vary from 200 to 5000 g/mol, corresponding to 3 to 110 oxyalkylene repeating units. The molecular weight of the polyester dispersants of type II can in particular vary from 500 to 20,000 g/mol, as determined by GPC.

Type II dispersants may further comprise one or more poly(oxy-C ₂ -C ₄ -alkylene) glycols, in particular polyethylene glycol or poly(ethylene-co-propylene) glycol, and/or an anionic surfactant, in particular an anionic surfactant bearing a sulfonate group or sulfate group. Examples of anionic surfactants include alkyl benzene sulfonate salts, alkyl sulfate salts and half sulfuric acid salts with C ₂ -C ₄ alkoxylated fatty alcohols, in particular ethoxylated or ethoxylated-co-propoxylated fatty alcohols, in particular alkali metal salts and ammonium salts.

Type III dispersants contain at least one oligo- or polyalkyleneimine, in particular at least one oligo- or poly-C ₂ -C ₄ -alkyleneimine, which is modified with a fatty acid, in particular a modified oligo- or polyalkyleneimine based on oligo- or polyalkyleneimine of the formula NH ₂ -A-NH-(A-NH) _k -A-NH ₂ where A is a C ₂ -C ₃ -alkylene and k is an integer from 0 to 50, in particular from 1 to 20 Suitable fatty acids for modifying the oligo- or polyalkyleneimine include C ₈ -C ₂₂ -alkanoic acids, C ₈ -C ₂₂ -alkenic acids and C ₈ -C ₂₂ -alkadienoic acids and mixtures thereof.

Preferred modified oligo- or polyalkyleneimines contain at least 50 wt. %, based on the total amount of modified oligo- or poly-C ₂ -C ₄ -alkyleneimine, compounds that can be described by the following formulas IIIa, IIIb, IIIc, IIId and IIIe:

Where

R' are identical or different and are selected from the group consisting of hydrocarbon radicals derived from a long chain fatty acid, and where R' is particularly selected from the group consisting of C ₇ -C ₂₁ -alkyl, C ₇ -C ₂₁ -alkenyl and C ₇ -C ₂₁ -alkanedienyl;

A represents C ₂ -C ₃ -alkylene, in particular 1,2-ethanediyl;

k represents 0 - 50, in particular 1 - 20, m represents k - 1, i.e. 0 - 49 and in particular 0 - 19.

One skilled in the art will understand that modified oligo- or polyalkyleneimines may also include compounds in which additional imino nitrogen atoms of the polyalkyleneimine are modified with a fatty acid radical or imidazoline radical, as described for formulas (IIIb), (IIIe) and (IIIe). Particularly preferred modified oligo- or polyalkyleneimines include at least one compound of formula (IIIc) or a mixture thereof with one or more compounds of formula (IIIa) or (IIIb), in particular a mixture wherein the compounds of formulas (IIIb) and (IIIc) constitute up to at least 30 wt. % based on the total weight of modified oligo- or polyalkyleneimines present in the dispersant.

Type III dispersants further contain one or more anionic surfactants bearing at least one poly(oxy-C ₂ -C ₄ -alkylene) group. Examples of such anionic surfactants include salts, in particular alkali metal salts and ammonium salts, half-esters of sulfuric acid with C ₂ -C ₄ -alkoxylated fatty alcohols, in particular with ethoxylated or ethoxylated-co-propoxylated fatty alcohols, and aliphatic half-esters of a dicarboxylic acid such as maleic acid, fumaric acid or succinic acid with a C ₂ -C ₄ alkoxylated fatty alcohol, in particular an ethoxylated or ethoxylated-co-propoxylated fatty alcohol.

If they are present in a microparticulate composition, the amount of dispersant is generally such that the weight ratio of dispersant, calculated as solids, and solid organic IR-absorbing pigment is in the range of 0.05:1 to 1: 1, preferably in the range from 0.1:1 to 0.8:1, in particular from 0.1:1 to 0.5:1.

According to one specific embodiment of the present invention, the microparticle compositions are in the form of an aqueous suspension. Such a suspension contains microparticles as a dispersed phase and an aqueous medium as a continuous phase. The aqueous suspension can be prepared by a microparticulate composition process as described herein. It can also be prepared by redispersing the microsolid composition as described herein in an aqueous medium.

The term "aqueous medium" refers to the liquid phase of the composition and contains the aqueous solvent and optionally dissolved compounds therein, for example dispersants as defined above, and, if present, one or more conventional formulation auxiliaries such as antifoaming agents or preservatives. The aqueous solvent of the aqueous suspension is water or a mixture thereof with a water-miscible organic solvent such as C ₁ -C ₄ alkanols, for example methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, isobutanol, or tert-butanol, C ₂ -C ₅ -alkanediols and C ₃ -C ₈ -alkanediols, preferably from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol and 1,4-butanediol. In general, the amount of water in one solvent is at least 50 wt. %, in particular at least 80 wt. % or at least 90 wt. %, based on aqueous solvent. The aqueous solvent may consist mainly of water, i.e. water is at least 95 wt. % of the total amount of solvent present in the suspension. The aqueous solvent may also be a mixture of the above water-miscible organic solvent and water. In the latter case, the mass ratio of water and water-miscible organic solvent in the aqueous solvent is preferably in the range of 99:1 to 1:1; more preferably is in the range of 50:1 to 3:1; and most preferably in the range from 20:1 to 4:1. The variously expressed amount of organic solvent can be from 1 to 50 wt. %, more preferably from 2 to 25 wt. % and most preferably from 5 to 20 wt. %, based on the total weight of the aqueous solvent.

The aqueous suspension will typically contain microparticles in an amount of at least 5 wt. %, and the amount can reach 45 wt. % or even more, 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. Often the aqueous suspension will contain microparticles in an amount of from 5 to 45 wt. %, preferably from 7 to 40 wt. %, in particular from 9 to 35 wt. %, 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. The pigment concentration in the aqueous suspension will often be in the range of 1 to 40 wt. %, in particular in the range from 2 to 25 wt. %, more specifically in the range from 3 to 20 wt. %, especially in the range from 4 to 15 wt. %, based on the total weight of the aqueous suspension.

If present, the concentration of one or more dispersants in the aqueous suspension is often in the range of 0.1 to 20 wt. %, preferably from 0.5 to 10 wt. %, in particular from 1.0 to 8 wt. %, based on the total mass of the aqueous suspension of microparticles.

The aqueous compositions of the present invention may also contain conventional auxiliaries, such as viscosity modifying agents (thickeners), antifoams, preservatives, buffers, inorganic dispersants, etc., which are commonly used in aqueous herbicide compositions. Such excipients may be included in the aqueous suspension after step ii) of the preparation process described herein has been carried out. The amount of additives, as a rule, should not exceed 10 wt. %, in particular 5 wt. % of the total mass of the aqueous suspension.

Antifoam agents suitable for the compositions of the present invention are, for example, silicone emulsions (such as, for example, Silicone SRE-PFL from Wacker or Rhodorsil ^® from Bluestar Silicones), polysiloxanes and modified polysiloxanes, including polysiloxane block polymers such as FoamStar products ^® SI and FoamStar ^® ST from BASF SE, long-chain alcohols, fatty acids, organofluorine compounds and mixtures thereof.

Suitable preservatives for preventing microbial damage to the compositions of the present invention include formaldehyde, p-hydroxybenzoic acid alkyl esters, 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 isothiazolinone preservatives, for example, are sold under the trade names Proxel ^® (Arch Chemical), Acticide ^® MBS (Thor Chemie) and Kathon ^® MK (Rohm & Haas).

If necessary, the compositions according to the present invention, in particular aqueous suspensions, may contain buffers to adjust the pH value. Examples of buffers are salts of alkali metals and 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 specific embodiment, the microparticulate composition of the present invention is in the form of a solid composition. Such a solid composition contains microparticles, optionally one or more dispersants, in particular the dispersants described herein as preferred. Solid compositions are presented, in particular, in the form of dispersible powders.

The solid composition can be prepared from the aqueous suspension that is initially formed in the process of preparing the microparticulate composition as described herein by removing the aqueous phase from the aqueous suspension. Removal of the aqueous phase can be achieved by separating the aqueous phase from the solid microparticles, for example by centrifugation or filtration. Preferably, the aqueous phase is removed by evaporation, such as spray drying or freeze drying.

As stated above, the method for preparing the microparticulate composition of the present invention includes a first step i) of providing an aqueous suspension of a solid organic IR absorbing pigment, which also includes an amino 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 compressed cake having a pigment concentration of typically 20 to 60% by weight. %, preferably from 30 to 55 wt. % and in particular from 35 to 50 wt. %, based on the total weight of the compressed cake. The compressed cake can be prepared by mixing particulate pigment with a suitable amount of water in the absence of any dispersant or in the presence of a dispersant to obtain a homogeneous material. Alternatively, the IR absorbing pigment may be introduced in step i) in the form of particles that are substantially free of water, for example in powder form.

Suitable amino-based 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, usually having at least two primary amino groups, such as, urea, thiourea, melamine, cyanoguanamine (= dicyandiamide), acetoguanamine and benzoguanamine. Precondensates can be partially or fully esterified, which means that the hydroxyl groups of the hemiaminal units formed by the reaction of the primary amino groups are esterified with an alcohol as well as a C ₁ -C ₆ alkanol such as methanol, ethanol, propanol, n-butanol, 2- butanol, isobutanol, n-pentanol or n-hexanol and/or C ₂ -C ₄ -alkanediol such as ethylene glycol. When curing conditions are applied, precondensates form cross-linked aminoplastic polymers.

Amino-based precondensates include, but are not limited to, condensation products of melamine and formaldehyde (melamine formaldehyde precondensates or MF precondensates), including fully or partially esterified MF precondensates, urea formaldehyde precondensates (UF precondensates), thiourea formaldehyde precondensates (TUF precondensates), melamine precondensates, urea and formaldehyde (MUF precondensates), including fully or partially esterified MUF precondensates, melamine, thiourea and formaldehyde precondensates (MTUF precondensates), including fully or partially esterified MTUF precondensates,

urea-glutaraldehyde precondensates, benzoguanamine-formaldehyde precondensates, dicyandiamide-formaldehyde precondensates and urea-lyoxal precondensates.

Suitable aminoplast precondensates for microencapsulation are known and can be found, inter alia, in Kirk-Othmer, Epicyclores of Chemical Technology, 3rd edition, Vol. 2, pp. 440-469, prior art cited above, 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 grades such as but not limited to Cymel® 303, 327, 328 or 385 (Cytec esterified melamine formaldehyde resins), Maprenal® grades such as but not limited to Maprenal® MF 900w/95, MF 915/75IB , MF 920/75WA, MF 921w/85WA, (Ineos esterified melamine formaldehyde resins), Kauramin® grades from BASF SE such as without limitation Kauramin® 783, Kauramin® 792 or Kauramin® 753 (melamine formaldehyde resins), Kauramin® 620 or Kauramin ® 621 (melamine-urea-formaldehyde resins), Kaurit® toT BASF SE types, such as without limitation Kaurit® 210, 216, 217, 220, 270, 285, 325 (aqueous solution of urea-formaldehyde resins), Luracoll® types, such as Luracoll® SD ( esterified melamine-formaldehyde resins), Luwipal® types such as, but not limited to, Luwipal® 063, Luwipal® 069 (esterified melamine-formaldehyde resins), or Plastopal® types, such as, but not limited to, Plastopal® BTM, Plastopal® BTW (esterified 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 from 1:0.8 to 1:4, in particular in the range from 1:1.5 to 1:4, especially in the range from 1 :2 to 1:3.5.

In suitable melamine-formaldehyde precondensates, which may be fully or partially esterified, the molar ratios of melamine to formaldehyde are generally in the range from 1:1.5 to 1:10, in particular in the range from 1:3 to 1:8, preferably in the range from 1:4 to 1:6.

In suitable melamine(thio)urea-formaldehyde precondensates, which can be fully or partially esterified, the molar ratios of melamine + urea or thiourea and formaldehyde are usually in the range from 1:0.8 to 1:9, in particular from 1:2 to 1: 8, preferably in the range from 1:3 to 1:6. The molar ratio of urea or thiourea to melamine is usually in the range from 5:1 to 1:50 and in particular in the range from 3:1 to 1:30.

Precondensates can be used in the form of esterified precondensates of an amino compound and an aldehyde. In these esterified precondensates, methylol groups are formed by the reaction of amino groups with formaldehyde and an alkanol or alkanediol, in particular with a C ₁ -C ₈ -alkanol, such as methanol, ethanol, n-propanol or n-butanol, in particular methanol, or C ₂ - With a ₄ -alkanediol such as ethylene glycol. The degree of esterification of these resins can be controlled by the molar ratio of amino groups and alkanol, which is usually in the range of 10:1 to 1:10, preferably in the range of 2:1 to 1:5.

The precondensates are particularly selected from the group consisting of melamine-formaldehyde precondensates, including fully or partially esterified melamine-formaldehyde precondensates and fully or partially esterified melamine-urea-formaldehyde precondensates and mixtures thereof. In particular, the pre-condensate is a fully or partially esterified melamine-formaldehyde condensate, which may contain small quantities, for example from 1 to 20 mol. % urea based on melamine.

The aqueous suspension according to step i) can be obtained by incorporating the particulate pigment and the aminoplast 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 microparticulate compositions of the present invention, in particular those described as preferred. The aqueous suspension may contain an amount of dispersant that is a portion or total amount to be included in the final microparticulate composition.

The aqueous suspension provided in step i) may contain additional excipients for the microparticulate compositions of the present invention, such as, in particular, one of the antifoaming agents described herein. In one embodiment of the present invention, part or all of the antifoam agent to be included in the final microparticulate composition is already present in the suspension.

The aqueous suspension contains an aminoplast-based precondensate in an amount that is typically in the range from 20 to 65 wt. %, in particular from 25 to 57 wt. % and especially from 27 to 52 wt. %, based on the total mass of aminoplast precondensate and organic IR-absorbing pigment, calculated as the organic solid.

In step i) the pigment is present in suspension in particulate form. The particle size distribution of the IR-absorbing organic pigment is typically characterized by a particle size that is smaller than the size of microparticles containing solid particles of IR-absorbing organic pigment that are surrounded by or included in the aminoplastic polymer. Often, the particle size distribution of the organic IR absorbing pigment has a D(v, 0.5) value of at most 0.8 µm, in particular at most 0.5 µm and especially at most 0.3 µm, e.g. in the range from 10 to 800 nm, in particular from 20 to 500 nm, more particularly in the range from 20 to 300 nm, as determined by static light scattering. However, in suspension, the IR absorbing organic pigment particles may form loose agglomerates and thus the apparent particle size may be larger. However, the size distribution of the primary IR absorbing organic pigment particles that form the agglomerate is typically characterized by D(v, 0.5) in the above ranges.

IR-absorbing pigments that are suitable for the microparticle compositions of the present invention can be obtained, for example, by chemical synthesis or from commercial sources that already have a suitable particle size distribution as well as an average particle diameter D (v 0.5 ) in the above ranges. In the event that the particles of the pigment used are too large, the particle size may be reduced using established particle crushing methods, including, but not limited to, crushing methods involving water or an organic solvent and grinding media such as beads or inorganic salts. Suitable methods and apparatus are known and are described, for example, in Perry's Chemical Engineers' Handbook, 7th ed. McGraw Hill 1997, 20-31 to 20-38, and the literature cited therein, and are commercially available, for example, from Netzsch Feinmahltechnik, FHZ GmbH, Hosokawa-Alpine AG, Willy A. Bachofen AG Maschinenfabrik, Coperion and Buhler GmbH.

The IR absorbing pigment present in the suspension of step i) may be deagglomerated during or preferably before step ii). Thus, the agglomerates of pigment particles contained in the suspension will be destroyed. Deagglomeration (sometimes also called disagglomeration) can be achieved by applying high shear forces to the suspension, for example using a dispersant or homogenizer such as disk homogenizers or rotor stator homogenizers, or by using ultrasound. Suitable homogenizers are well known and commercially available, for example from Netzsch Feinmahltechnik or from IKA-Werke GmbH&Co. KG. The use of ultrasound for deagglomeration of particles in the liquid phase has often been described, for example in WO 99/32220 or in U Teipel et al., Int. J. Mineral Processing Vol.74, Supplement (2004), S183-S190. Deagglomeration is usually continued until a particle size distribution as well as an average particle diameter D (v 0.5) is obtained within the above ranges.

The aqueous suspension is prepared in step i) under conditions that preclude any significant polycondensation of the aminoplast-based precondensate at this step. This is particularly achieved by adjusting the pH value to at least pH 6, for example from pH 6 to pH 9. In order to obtain a homogeneous mixture of the components of the aqueous suspension, i.e. pigment particles, typically a detergent, an amino-based precondensate and optionally auxiliary substances such as, in particular, an antifoaming agent, are combined and vigorously mixed using typically a high-performance mixer such as, in particular, high-speed toothed disc dispersants. peripheral tip speed (eg from Vollrath GmbH), Ultra-turrax dispersants (IKA®-Werke GmbH & Co) and/or ultrasonic devices such as ultrasonic tips. Preferably the mixture is dispersed using a disc disperser or, alternatively, first dispersed using an Ultra-turrax disperser and then treated with an ultrasonic cooler.

In step ii) of the method according to the present invention for preparing the microparticulate composition according to the present invention, the polycondensation of the aminoplast precondensate in the aqueous suspension obtained in step i) is carried out in the presence of one or more surfactants, which are preferably selected from dispersants, described herein as optional components of the microparticle compositions of the present invention. Thus, depending on the amount of such dispersant already added to the suspension in step i), additional amount of dispersant may be added in step ii) to the full amount of dispersant to be included in the final microparticulate compositions. However, preferably the amount of dispersant to be included in the final composition has already been added in step i).

Accordingly, it is preferred that one or more surfactants contained in the aqueous suspension in which the polycondensation is carried out in step ii) are selected from the dispersants described herein as optional components of the microparticulate composition of the present invention. One or more surfactants, i.e. one or more dispersants as defined in the present invention are typically used in such an amount in step ii) that the weight ratio of surfactant to solid organic IR absorbing pigment is in the range of 0.05:1 to 1:1, preferably in the range from 0.1:1 to 0.8:1, in particular from 0.1:1 to 0.5:1.

The concentration of the aminoplast precondensate in the aqueous suspension subjected to polycondensation in step ii) is often in the range of 0.5 to 30 wt. %, preferably from 1.0 to 25 wt. %, in particular from 2.0 to 20 wt. %, based on the total weight of the suspension.

The pigment concentration in the aqueous suspension subjected to polycondensation is generally in the range from 1 to 40 wt. %, in particular in the range from 2 to 25 wt. %, more specifically in the range from 3 to 20 wt. %, especially in the range from 4 to 15 wt. % of the total mass of the suspension.

The polycondensation of the aminoplast based precondensate can be carried out in a well known manner, for example by adjusting the pH value of the suspension obtained in step i) to a value of at most pH 5.5 and heating it to a certain reaction temperature, which are suitable conditions for initiating and carrying out the polycondensation . During polycondensation, the amino-based precondensate is converted into a water-insoluble amino-plastic resin, which precipitates from the aqueous phase and deposits preferentially on the surface of the solid pigment material, thereby incorporating or surrounding the pigment particles to produce pigment-polymer particles.

According to the present invention, the aminoplast polycondensation is carried out at a pH value of at most pH 5.5, in particular at a pH value of at most pH 5, especially at a pH value of at most pH 4, for example in the range of pH 0 to 5, more particularly in the range of pH 1 to 4 or in the range from pH 2 to 4.

The pH of the aqueous suspension is usually adjusted by adding suitable amounts of organic or inorganic acid such as sulfuric acid, hydrochloric acid, phosphoric acid, carboxylic acid including alkanoic acids, alkanedionic acids or hydroxycarboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid acid, malic acid or citric acid, and alkyl or arylsulfonic acids such as methanesulfonic acid or toluenesulfonic acid. Preferably, the acid catalyst is selected from the group consisting of formic acid, sulfuric acid, methanesulfonic acid and hydrochloric acid, and in particular formic acid. It is preferable, but not necessary, for at least a portion, in particular a majority, of the acid to be present in the aqueous suspension before the aqueous suspension is heated to reaction temperature.

Preferably, the polycondensation of the aminoplast-based precondensate is carried out at elevated temperatures, in particular at a temperature of at least 50°C, in particular at least 60°C and can reach 100°C. Preferably, the temperature at which polycondensation of the aminoplast-based precondensate occurs does not exceed 95°C, in particular 90°C, and is preferably in the range from 50 to 95°C, in particular in the range from 60 to 90°C or in the range from 70 to 90°C. It is possible to initiate the polycondensation of the aminoplast at a relatively low temperature, for example at a temperature in the range of 40 to 60°C, and then complete the polycondensation reaction at a higher temperature, for example, from 60 to 95°C or from 70°C to 90°C.

The time for completion of polycondensation can vary depending on the reactivity of the precondensate, the temperature and pH value of the aqueous suspension and can take from 0.3 hours to 10 hours, in particular from 0.5 hours to 5 hours.

The aqueous suspension of pigment-polymer particles thus obtained can be neutralized by adding a base. Preferably, the pH of the suspension is adjusted to a pH value of at least 6, for example a pH value in the range from pH 6 to 10, in particular in the range of pH values from 6.5 to 9.0. Suitable bases include, but are not limited to, organic amines, in particular water-soluble amines such as mono-, di- and triethanolamine. However, an inorganic base such as potassium hydroxide or sodium hydroxide can be used. However, for the purposes of the present invention such neutralization is not required.

Aqueous suspensions of pigment-polymer particles that can be prepared by the process of the present invention qualify as microparticulate compositions of the present invention. In these aqueous suspensions, the pigment-polymer particles contain the pigment and an aminoplastic resin that surrounds or includes the pigment.

Aqueous suspensions of pigment-polymer particles further contain one or more surfactants as defined above, which are preferably selected from the dispersants detailed herein, such as, in particular, those mentioned as preferred.

From aqueous suspensions prepared by the method 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 lyophilized to obtain a solid composition in the form of a powder or granules. The solid composition may be re-suspended or formulated using formulation auxiliaries as described herein, such as, for example, viscosity modifying agents (thickeners), antifoaming agents, preservatives, buffers, inorganic dispersants and others that are commonly used in aqueous compositions.

The microparticle compositions of the present invention in the form of an aqueous suspension of microparticles, as well as in the form of a solid microparticle composition, such as powders, can be used for printing ink compositions that are particularly suitable for security printing.

A security feature, for example for security documents, can be classified into “hidden” and “open” security features. The protection provided by covert security features is based on the concept that such features are hidden, usually requiring special equipment and knowledge to detect them, whereas "overt" security features are easily detected by unaided human capabilities, e.g. such features can be visible and/or detected using tactile sensations, but at the same time they are difficult to reproduce and/or copy

Security printing of a "latent" security feature typically involves printing on a substrate an image that is invisible or otherwise undetectable under environmental conditions and that can be visualized or detected by applying a suitable stimulus. The stimulus can be, for example, electromagnetic radiation or heat.

In particular, the printing compositions of the present invention make it possible to coat or print a secure image on a substrate. Since the printing composition of the present invention contains an IR absorbing pigment, these pigments are therefore also part of the image coated or printed on the substrate. Using devices capable of measuring IR radiation, an otherwise undetectable image can then be detected based on the degree of absorption of IR radiation, particularly emitted wavelengths in the range of 750 to 1100 nm, especially in the range of 790 to 1100 nm. In this way, a specific security image on the substrate can be identified.

The printing compositions in accordance with the present invention are particularly suitable for this type of security printing, since they produce security images showing reflection of radiation with wavelengths in the range from 750 to 1100 nm, especially from 790 to 1100 nm, which is reduced by at least 40%, in particular at least 50%, compared to the empty substrate.

The printing ink compositions of the present invention, in particular those useful for security printing, contain, in addition to the microparticulate composition as defined herein, a binder which, in principle, can be selected from any binder known in the art. of the art which is suitable for the formulation of printing inks. More specifically, the binders for the printing ink compositions of the present invention are selected from binders that are either radiation curable, can be thermally dried, or can be oxidatively dried, and accordingly provide ink compositions that are either radiation curable, or can be thermally dried, or can be dried oxidatively. Oxidatively drying binders and oxidatively drying inks derived from them are particularly preferred in the context of the present invention.

Examples of radiation-curable binders, such as in particular UV-curable binders, are binders containing oligomers and monomers with ethylenically unsaturated double bonds. 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 which have a (poly)urethane structure and have acrylic or methacrylic groups, for example, reaction products of polyisocyanates with hydroxy-functionalized acrylic or methacrylic compounds, and mixtures thereof. Preferably, the oligomers are polyester acrylates, urethane acrylates, and mixtures thereof. Monomers are usually selected from esters of acrylic acid with mono- and 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, etc. trahydrofurfuryl acrylate, 4-tert-butylcyclohexyl acrylate, 4-hydroxybutyl acrylate and trimethylol formal 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, in particular, long oil alkyd resins, polyamide resins, (meth)acrylic resins, polyurethane resins, phenolic resins, vinyl resins, rosin-modified maleic resins and varnishes, heat-treated resins such as alkyd, polyurethane or phenolic resins with an oxidatively drying oil such as tung oil, linseed oil, poppy seed oil or perilla oil, and mixtures of these resins and varnishes. The above-mentioned resins and varnishes are well known and, for example, are described in more detail in R. van Gorkum et al., Coordination Chemistry Reviews 249 (2005) 1709-1728; J. F. Black, J. Am. Chem. Soc, 1978, 100, 527, J. Mallegol et al., Prog. Org. Coatings 39 (2000) 107 - 113, The Printing ink manual, RH Leach and RJ Pierce, Springer Edition, ^5th Edition, and are commercially available, for example from Epple Druckfarben AG.

Security inks containing microparticles disclosed herein may be

- oxidatively drying protective ink containing, in addition to microparticles and oxidatively drying binder(s), from about 0.01 to about 10 wt. % based on the total weight of oxidatively drying security inks, one or more drying agents, or

- UV-visible light-curable security ink containing, in addition to microparticles and UV-visible light-curable binder(s), from about 0.1 to about 20 wt. % based on the total weight of the UV-visible light-curable security ink, one or more photoinitiators, or

- thermally drying security ink containing, in addition to microparticles and thermally drying binder(s), from about 10 to about 90 wt. % based on the total weight of the thermally drying security ink, one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, or

combination of the above security inks.

Particularly preferred according to the present invention are printing ink compositions containing at least one oxidation-drying binder, which is particularly selected from alkyd resins, such as, in particular, fatty alkyd resins, polyamide resins, (meth)acrylic resins, vinyl resins, maleic resins modified with rosin, varnishes obtained by heat treatment of alkyd, polyurethane or phenolic resins 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 compositions of the present invention typically contain additional auxiliaries and components that are typically included in inks, such as, for example, pigments and dyes, fillers, for example, alumina, calcium carbonate or china clay, colorants, for example, cobalt carboxylate or carboxylate. manganese, solvents, surfactants, waxes, UV stabilizers, photoinitiators, antioxidants, emulsifiers, slip agents, etc.

In the following compositions A D, which serve as specific examples of the printing ink compositions of the present invention, the individual components have the meanings defined herein, in particular the preferred meanings.

Composition A: Composition of oxidatively drying gravure ink:

10-30 wt. % oxidatively drying resin;

0-15 wt. % pigment;

1-10 wt. % of a microparticle composition according to the present invention containing an organic IR absorbing pigment, preferably in the form of a solid microparticle composition;

10-50 wt. % filler;

5-20 wt. % solvent;

0.1-3 wt. % drying agent;

1-7 wt. % wax;

1-10 wt. % surfactant;

0.1-5 wt. % additives, e.g. slip agent, antioxidant or stabilizer.

Composition B: UV-curable gravure ink composition:

20-35 wt. % oligomers;

10-30 wt. % monomers;

0-20 wt. % pigment;

1-10 wt. % of a microparticle composition according to the present invention containing an organic IR absorbing pigment, preferably in the form of a solid microparticle composition;

10-50 wt. % filler;

1-10 wt. % photoinitiator;

1-3 wt. % UV stabilizer;

1-5 wt. % additives, for example, emulsifier.

Composition C: Composition of thermosetting or heat-drying gravure ink:

25-35 wt. % thermally drying resin;

0-5 wt. % pigment;

1-10 wt. % of a microparticle composition according to the present invention containing an organic IR absorbing pigment, preferably in the form of a solid microparticle composition;

45-50 wt. % filler;

10-15 wt. % solvent;

0.5-2 wt. % drying agent;

1-5 wt. % wax.

Composition D: Composition of oxidative drying ink for offset printing:

20-40 wt. % Varnish I: oxidatively drying resin such as alkyd resin;

30-50 wt. % varnish II: an oxidatively drying resin obtained by heat treating 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 wt. % pigment;

1-10 wt. % of a microparticle composition according to the present invention containing an organic IR absorbing pigment, preferably in the form of a solid microparticle composition;

1-7 wt. % wax;

0.1-0.5 wt. % antioxidant;

1-5 wt. % drying agent.

The present invention also relates to a method for producing a security feature or a security document, which includes applying a printing ink composition to a substrate by a printing method.

The printing ink compositions of the present invention can be applied by a printing process preferably selected from the group consisting of offset printing processes, rotogravure printing processes, silk screen printing processes, gravure flat plate printing processes, flexographic printing processes, letterpress printing processes; more preferably offset printing processes and gravure printing processes from flat copper plates. The above printing techniques are well known to those skilled in the art.

In this context, the term "security feature" means, in particular, a specific image printed on a substrate; and the term "substrate" means any object that is intended to provide a security feature or is intended to be converted into a security document by application of an ink composition to provide a security feature.

The term "secure document" means any document designed to protect against forgery or counterfeiting. Such protected documents include, but are not limited to, valuable documents and valuable commercial goods. Typical examples of valuable documents include, for example, banknotes, documents, tickets, checks, vouchers, fiscal stamps and tax labels, agreements and the like, identification documents such as passports, identity cards, visas, driver's licenses, bank cards, credit cards, protocols, documents or access cards, entrance tickets, public transport tickets or titles, etc., preferably banknotes, identity documents, proof of entitlement, driving licenses and credit cards. The term "high value commercial item" refers to packaging materials, in particular for cosmetics, nutraceuticals, pharmaceuticals, alcohols, tobacco, beverages or food, electrical/electronic products, textiles or jewelry, i.e. products that must be protected against counterfeiting and/or illegal reproduction to ensure the contents of the packaging, such as genuine medicines. Examples of such packaging materials include, for example, labels such as authentication labels, tamper evident labels and seals. It should be noted that the disclosed substrates, valuable documents and valuable commercial items are provided for illustrative purposes only, without limiting the scope of the present invention.

Alternatively, the printing ink composition of the present invention containing microparticles that include an organic IR absorbing pigment can be printed on an auxiliary substrate such as, for example, a security thread, a security strip, a foil, a decal, a window or a label, and subsequently transferred to the protected document in a separate stage.

In addition to being used to protect and authenticate a security document as described above, the printing ink compositions of the present invention can also be used for decorative purposes by applying the compositions to objects or elements to be decorated. Common examples of such objects or items include, for example, luxury goods, cosmetic packaging, automobile parts, electronic/electrical appliances, furniture, and nail polishes.

Accordingly, the present invention also relates to security documents as well as decorative objects that contain a substrate onto which a printing ink composition according to the present invention is applied through a printing process.

Fig. 1: The chart shows the relative absorption reduction calculated from the print reflectance measured at the maximum absorption of the printing ink of the present invention and the comparative printing ink of Application Example 3.

Particle size distribution (PSD) was determined by laser diffraction using a Malvern Mastersizer 2000 in accordance with European standards ISO 13320: 2009 EN. Data were processed according to Mie-Theory using software using 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.

Precondensate based on aminoplast A: 70 wt. % aqueous solution of methylated melamine formaldehyde precondensate: Luracoll® SD, BASF SE.

Pigment A: An IR-absorbing pigment based on a nickel dithiolene complex of formula (I), where R ¹ , R ² , R ³ and R ⁴ are aryl: CAS name [nickel(P), bis(diphenylimidazolidintrition-κS4, κS5- ), (SP-4-1)-].

Pigment B: IR-absorbing pigment based on copper naphthalocyanine complex according to formula B-6 from EP 3067216.

Pigment C: An IR absorbing pigment based on a nickel dithiolene complex of formula (I) wherein R ¹ , R ² , R ³ and R ⁴ are methyl.

Pigment D: An IR-absorbing nickel dithiolene complex pigment of formula (I) wherein R ¹ , R ² , R ³ and R ⁴ are isopropyl.

Dispersant A: commercially available type I dispersant (40 wt.% aqueous solution of a copolymer having repeating units of butyl acrylate, methyl polyethylene oxide acrylate and vinyl pyridine, prepared according to example A6 in WO 2006/074969).

Dispersant B: Type III dispersant (water-containing mixture of fatty acid-modified pentamethylenehexamine and ethoxylated fatty acid maleic acid half-ester having a solids content of 97% by weight).

Antifoam agent A: modified polydimethylsiloxane: Foamstar® SL 2280, BASF SE

Examples of receiving:

Example 1a:

29.91 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 12.25 g of aminoplast precondensate A in 108.53 g of water . This mixture was pre-dispersed using Ultra-turrax and then sonicated using an ultrasonic tip while cooling with ice for 10 minutes. Then, 4 g of formic acid aqueous solution (20 wt%) was added. The mixture was stirred for 1 hour at room temperature. The temperature was then raised at 80°C for 1 hour, maintained at 80°C for 2 hours, and then cooled to room temperature. A dispersion of encapsulated pigment was obtained. Representative values for the particle size distribution and the relative amount of pigment relative to the aminoplast are given in Table 1. This dispersion was then dried to obtain a fine powder.

Examples 1b and 1c were prepared similarly to Example 1a. The characteristic values of the particle size distribution are given in Table 1.

Example 2:

33.12 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 9.19 g of aminoplast precondensate A in 105.82 g of water . This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 3:

32.05 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 10.21 g of aminoplast precondensate A in 106.72 g of water . This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 4:

30.98 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 11.23 g of aminoplast precondensate A in 107.63 g of water . This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 5:

28.85 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 13.27 g of aminoplast precondensate A in 109.5 g of water . This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 6:

27.78 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 20 g of dispersant A and 0.4 g of antifoam A, and 14.29 g of aminoplast precondensate A in 109.5 g of water . This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 7:

155.44 g of wet cake of pigment A (38.60 wt.% pigment) was mixed with 25 g of dispersant A and 2.0 g of antifoam A, and 81.66 g of aminoplast precondensate A in 449.55 g of water . This mixture was dispersed using a disk disperser at a mixing speed of 10,000 rpm. Then 20 g of 20 wt. % formic acid solution was added. The mixture was stirred for 1 hour at room temperature. This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 8:

29.91 g of wet cake of pigment A (46.8 wt.% pigment) was mixed with 5.0 g of dispersant A and 0.4 g of antifoam A, and 12.25 g of aminoplast precondensate A at 63.55 g water. This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Example 9:

33.10 g of wet cake of pigment A (42.3 wt.% pigment) was mixed with 8.24 g of dispersant B and 0.4 g of antifoam A, and 12.25 g of aminoplast precondensate A in 63.55 g water. This mixture was then processed in the same manner as described in example 1a. The characteristic values of the particle size distribution and the relative amount of pigment in relation to the aminoplast are given in Table 1.

Compositions of pigments B, C and D based on microparticles can be obtained similarly to the methods described in examples 1a - 9.

Application examples:

Application example 1: Preparation of ink composition for offset printing (general procedure):

1 part of the solid powder microparticle composition of the present invention was included in 9 parts of a commercial oxidative drying blanket varnish. The mixture was homogenized in a three-roll mill.

Application example 2: Comparison of inks with installed IR absorption:

The composition of offset ink according to the present invention, consisting of 10 wt. % solid composition of microparticles according to Example 1a in a commercial oxidation-drying offset varnish (Glanzdrucklack 1188, Epple AG) was prepared as described above. The ink was applied to paper (APCO II/II paper; Fogra Forschungsgesellschaft Druck e.V.) using offset printing equipment (Prtifbau). Accordingly, the resulting ink composition, including 4 wt. % non-encapsulated pigment A was chosen as a comparative composition and printed because it was found to provide offset printing on paper having almost the same IR reflectance in the wavelength range of 750 - 1100 nm as the ink composition print of the present invention when measured using a NIR spectrometer (Datacolor 45IR) directly after printing. Both prints were measured again after 20 days. The results obtained showed that after this period, the increase in reflectance of prints prepared using the comparative inks was 25% higher than the increase in reflectance of prints prepared using the inks of the present invention (measured at maximum ink absorption).

Application example 3: Comparison of prints made using inks having the same pigment concentration:

The offset ink composition of the present invention, consisting of a solid microparticle composition according to Example 1a in non-commercial oxidation-drying offset varnishes, was prepared as described above. The pigment concentration was 4 wt. %. Comparative ink was prepared in a similar manner, but using non-encapsulated pigment A at a pigment concentration of 4 wt. %. The ink composition of the present invention and the comparative ink composition were printed on paper (APCO II/II paper; Fogra Forschungsgesellschaft Druck eV) using offset printing equipment (Prufbau) so that in each case the ink concentration was 2 g/m ² (content pigment 4%) paper. The infrared reflectances of the prints in the wavelength range from 750 to 1100 nm were monitored for 20 days using an NIR spectrometer (Datacolor 45IR). The relative absorption decrease measured at maximum ink absorption (calculated based on reflectance) is shown in FIG. 1.

Application Example 4: Comparing Prints Using Inks of the Same Pigment Concentration

The oxidation-drying offset ink composition of the present invention, consisting of the solid microparticle composition of Example 7 in a commercial oxidation-drying offset varnish (Matt 2154, Epple AG), was prepared as described above. The pigment concentration was 4 wt. %. Comparative ink was prepared in a similar manner, but using non-encapsulated pigment A at a pigment concentration of 4 wt. %. The ink composition of the present invention and the comparative ink composition were printed on paper (APCO II/II paper; Fogra Forschungsgesellschaft Druck eV) using offset printing equipment (Prufbau) so that in each case the ink concentration was 1 g/m ² (content pigment 4%) paper. The IR reflectances of the prints in the wavelength range from 750 to 1100 nm were measured using an NIR spectrometer (Datacolor 45IR) immediately after printing and after 6 days. During this period, the reflectance of the print produced with the comparative ink increased by 37% compared to the measured initial reflectance, while that of the print produced with the ink of the present invention increased by only 7%.

Claims (39)

1. A microparticle-based pigment composition of an organic IR-absorbing pigment, which is a polyunsaturated organic compound or an organometallic compound having a major absorption maximum in the range from 750 to 1100 nm, where the microparticles of the pigment composition contain an organic IR-absorbing pigment in the form of solids particles that are surrounded by or included in an aminoplastic polymer that is a polycondensation product of one or more amino compounds and one or more aldehydes, wherein the microparticle-based pigment composition has a volumetric particle size distribution, as determined by static light scattering, having a volume average a D(4.3) value in the range of 1.0 to 15.0 μm, wherein the amount of aminoplastic polymer in the microparticle composition is from 15 to 50 wt.%, based on the total weight of the aminoplastic polymer and the organic IR-absorbing pigment, and wherein the amount of the organic IR-absorbing pigment is from 50 to 85 mass% based on the total weight of the aminoplastic polymer and the organic IR-absorbing pigment, wherein the aminoplastic polymer is a melamine-formaldehyde resin. 2. The composition according to claim 1, where the organic IR-absorbing pigment is selected from the group consisting of dithiolene metal complexes, phthalocyanine pigments, naphthalocyanine pigments, rylene pigments, polymethine pigments, anthraquinone pigments and mixtures thereof. 3. The composition according to claim 2, wherein the organic IR-absorbing pigment is selected from the group consisting of dithiolene metal complexes of formula (I), Where M represents Ni, Pd or Pt, X ¹ , X ² , independently of each other, represent O or S, R ¹ , R ² , R ³ , R ⁴ are the same or different and are selected from the group consisting of alkyl, where one or more non-adjacent CH ₂ alkyl radicals may be substituted by O, alkenyl, aryl and hetaryl, where aryl and hetaryl are unsubstituted or substituted, and naphthalocyanine complexes of formula (II) Where M ¹ represents Cu, Fe, Mn, Pd, Pt, VO, Si(OR ⁸ )2, Al(R ⁷ ) or Ga(R ⁷ ), R ⁵ represents H, F, OR ⁹ , SR ⁹ , NHR ¹⁰ , NR ¹⁰ R ¹¹ , R ⁶ represents H, F, OR ⁹ , SR9, NHR ¹⁰ , NR ¹⁰ R ¹¹ , R ⁷ is selected from the group consisting of Cl, OH and OR ¹² ; R ⁸ is selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _m -R ¹³ and phenyl; R ⁹ is selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _m -R ¹³ and phenyl; R ¹⁰ , R ¹¹ are independently selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _n -R ¹³ and phenyl, or R ¹⁰ , R ¹¹ together form a 5- or 6-membered saturated N-heterocyclic ring, which is optionally substituted with 1 or 2 methyl groups; R ¹² is selected from the group consisting of C ₁ -C ₁₂ -alkyl, (C ₂ H ₄ O) _n -R ¹³ and phenyl; R ¹³ is C ₁ -C ₁₂ alkyl, and n, m independently represent 0, 1, 2, 3 or 4. 4. The composition according to claim 1, which further contains at least one dispersant selected from the group consisting of - nonionic or anionic polymeric dispersants having a plurality of poly(oxy-C ₂ -C ₄ -alkylene) groups, - acidic polyethers containing ester groups bearing at least one poly(oxy-C ₂ -C ₄ -alkylene) group, or mixtures thereof with poly(oxy-C ₂ -C ₄ -alkylene) glycols and/or anionic surface - active substances, and - mixtures of modified polyamines with anionic surfactants bearing at least one poly(oxy-C ₂ -C ₄ -alkylene) group. 5. Composition according to any one of claims 1-4, which is an aqueous suspension of microparticles. 6. The composition according to any one of claims 1-4, which is a solid composition of microparticles. 7. A method for producing a microparticle-based pigment composition according to any one of claims 1 to 6, which includes the following steps: i) providing an aqueous suspension of solid organic IR-absorbing pigment particles that also contain an amino-based precondensate of one or more amino compounds and one or more aldehydes; ii) carrying out the polycondensation of the aminoplast-based precondensate in an aqueous suspension of a solid organic IR-absorbing pigment in the presence of at least one surfactant. 8. The method according to claim 7, wherein the particles of the solid organic IR absorbing pigment in the aqueous suspension have a volume particle size distribution as determined by static light scattering, having a volume average particle diameter D(v 0.5) of at most 0, 8 microns. 9. The method according to claim 7, where the mass ratio of surfactant and solid organic IR-absorbing pigment is in the range from 0.05:1 to 1:1. 10. Method according to any one of claims 7 to 9, wherein the aqueous suspension of the solid organic IR absorbing pigment is deagglomerated before step ii). 11. Use of a microparticle composition according to any one of claims 1 to 6 to obtain a printing ink composition for security printing. 12. A printing ink composition comprising a microparticle-based pigment composition according to any one of claims 1 to 6 and a binder. 13. The composition of printing ink according to claim 12, intended for security printing. 14. The printing ink composition of claim 12 or 13, wherein the binder contains at least one oxidatively drying resin. 15. A method for producing a security feature or a security document, which includes applying a printing ink composition according to one of claims 12 to 14 onto a substrate through a printing process. 16. The method of claim 15, wherein the printing process is selected from the group consisting of flat copper plate gravure printing, offset printing, gravure printing (also known as rotogravure), silk screen printing, flexographic printing and combinations thereof, preferably by gravure printing with flat copper plates, offset printing or silk screen printing, more preferably by intaglio printing from flat copper plates. 17. A security document comprising a substrate onto which the printing ink composition according to one of claims 12 to 14 has been applied by a printing process.