Pigment preparations for use in low viscosity security inks

Abstract

The present invention relates to the use of a pigment preparation for security applications, or in low viscosity security inks, said pigment preparation comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophtalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm, wherein the low viscosity security inks are selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks. The low viscosity security inks, comprising the pigment preparation, having altogether advantageous performance properties, especially high color strength and excellent absorption characteristics paired with good dispersion stability and low sedimentation. A high penetration depth is achieved when used in dyeing paper, cellulose etc.

Description

[0001] BASF SE 231030 1 Pigment preparations for use in low viscosity security inks DESCRIPTION The present invention relates to the use of a pigment preparation for security applications, or in low viscosity security inks, said pigment preparation comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophtalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm, wherein the low viscosity security inks are selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks. The low viscosity security inks, comprising the pigment preparation, having altogether advantageous performance properties, especially high color strength and excellent absorption characteristics paired with good dispersion stability and low sedimentation. A high penetration depth is achieved when used in dyeing paper, cellulose etc. TECHNICAL BACKGROUND JP2004196893A relates to a yellow inkjet ink composition comprising: at least a yellow organic pigment PY138, a derivative of PY138, and water, wherein the derivative of PY138 has one sulfonic acid group that is salt-bonded to an alkali ion, and the proportion of water in the total solvent is 50 wt.% or greater. JP2006348205A relates to an activation energy radiation-curable inkjet ink comprising a quinophthalone derivative containing a polymeric dispersing agent, a monomer, a quinophthalone pigment, and a sulfonic acid or salt thereof JP2012077192A relates to a method for selecting or designing a pigment derivative that provides a pigment composition having good dispersibility in a pigment composition obtained by treating a pigment with the pigment derivative, the method comprising the steps of: measuring or calculating a dipole moment of the pigment derivative; selecting a pigment derivative from the measured or calculated dipole moment values or designing a pigment derivative from the dipole moment values. EP1672039A1 (CN1777659A) relates to a method of producing a water-based pigment dispersion for ink-jet ink, comprising: a kneading process for kneading a mixture containing a styrene-based resin, a quinacridone-based pigment, a phthalimidomethylated quinacridone-based compound, such as, for example, a compound of formula (I): BASF SE 231030 2 in an aqueous medium, wherein the styrene-based resin has 60% by mass or more of a styrene-based monomer unit based on all monomer components, a monomer unit containing an unsaturated aliphatic carboxylic acid having a radical polymerizable double bond, an acid value of 50 to 300 and a weight-average molecular weight of 7500 to 40000. US2012 / 004348A1 relates to a solid pigment preparation, comprising, all based on a total weight of the preparation: (A) at least 60% by weight of a pigment component comprising at least one selected from the group consisting of a pigment and a filler; (B) 1% by weight to 29% by weight of a surface-active additive component based on at least a phosphoric or phosphonic ester, which is anionic or nonionic; (C) 1% by weight to 29% by weight of at least one nonionic surface-active additive comprising at least one polyether selected from the group consisting of a propylene oxide homopolymer, an ethylene oxide-propylene oxide block copolymer with terminal blocks consisting of at least one propylene oxide unit, an ethylene oxide adduct onto at least one mono- or bifunctional amine or alcohol wherein a length of an ethylene oxide chain thereof is adjusted such that the adduct is water-insoluble, and an ethylene oxide-propylene oxide block copolymer adduct onto at least one mono- or bifunctional amine or alcohol with at least one terminal block consisting of at least one propylene oxide unit; (D) 0% by weight to 20% by weight of an additive component comprising at least one further additive other than additives of the components (B) and (C), wherein a sum total of the weight percentages does not exceed 100% by weight. JP5834389B2 relates to a production method of a resin composition for a color filter, the composition containing a pigment, a pigment dispersant, a pigment derivative, a binder component and a solvent, and the method includes steps of: preparing a pigment dispersion liquid by dispersing a pigment in a solvent in the presence of a pigment dispersant; preparing a pigment derivative solution by dissolving or dispersing an imide-alkylated derivative of a pigment having a specified imide alkyl group in a solvent; and mixing the pigment dispersion liquid, the pigment derivative solution and a binder component. BASF SE 231030 3 US20060112852 (WO200450770) relates to solid pigment preparations, comprising (A) at least one organic pigment, such as for example, C.I. Pigment Red 254, C.I. Pigment Violet 23, C.I. Pigment Green 7 and 36; (B) at least one pigment derivative, such as, for example, quinophthalone sulfonic acidsof the formula (Ia),(C) at least consisting of the nonionic polyethers comprising no primary amino group, said polyethers' acidic phosphoric, phosphonic, sulfuric and / or sulfonic esters, the salts of these esters and the alkyl- and alkylarylsulfonic acids, their salts and their condensation products with formaldehyde. Examples of materials which can be pigmented with the pigment preparations materials are, for example, paper, paperboard, cardboard, wood and woodbase, which can each be coated or otherwise finished. US20090121201A1 (WO2006 / 114403A2) relates to green pigment preparations comprising as major constituents(A) C.I. Pigment Green 36 ( ),(B) at least one pigment the sulfonic acid derivatives of (C) if desired, at least one surface-active agent different from (B), obtainable by salt kneading or salt grinding of pigment (A) in the presence of pigment derivative (B); and to a method for producing the green component of a color filter, comprising the step of applying the pigment preparation. Preference is given to quinophthalone derivatives known from WO02 / 00643, particularly the sulfonic acid derivatives and salts thereof that are described therein. BASF SE 231030 4 Quinophthalone derivatives especially suitable as component (B) are derived from C.I. Pigment Yellow 138 and have the following formula , in which Y is hydrogen or is one of the above- As component (C) it is possible to use polymeric surface-active agents, preference being given to anionic and nonionic surface-active agents. JP2012193318A relates to compositions, which are useful for color filters and are manufactured by kneading C.I. Pigment Yellow 138 (I), dispersing agents [ II; n = 1-5; R1 = H, (substituted) alkyl; salts (A), and A-insoluble aqueous WO2006 / 117342 relates to the use of solid pigment preparations which contain as essential constituents (A) 30 to 90% by weight of at least one pigment and (B) 10 to 70% by weight of at least one water-soluble surface-active additive for colouring cellulose / polymer composite materials, and a process for producing colored cellulose / polymer composite materials, which comprises using cellulose particles which have been colored with the pigment preparations. WO2013079521A1 relates to the field of authentication of coating compositions such as varnishes, inks and paints, and it is particularly useful in the field of authentication of such coating compositions when applied to substrates like banknotes or other valuable documents. It is particularly directed to a marked coating composition, e.g. an ink, that is marked with a marker (taggant) such as to allow for its authentication, and a method for authenticating such a marked coating composition. The marking is achieved by covalently binding a taggant to a coating composition component, e.g. such used for BASF SE 231030 5 security documents. The taggant, which is not extractable through usual chemical treatments like washing methods or the use of solvents, can be detected and identified upon thermally induced chemical fragmentation with a PY-GC-MS apparatus. It is an object of the present invention to provide low viscosity security inks, comprising a pigment preparation, having altogether advantageous performance properties, especially high color strength and excellent absorption characteristics. The pigment should be homogeneously dispersed and the security inks should show no or low sedimentation despite their low viscosity. A high penetration depth should be achieved when used in dyeing paper, cellulose etc. In a first aspect the present invention relates to the use of a pigment preparation, comprising (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophthalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm, in low viscosity security inks selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks. In a second aspect the present invention relates to the use of a pigment preparation for security applications, said pigment preparation comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophthalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm. In a third aspect the present invention relates to a low viscosity security ink selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks, comprising a pigment preparation, which comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophthalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm. BASF SE 231030 6 The pigment preparation is obtainable by salt kneading or salt grinding of the organic pigment (A) in the presence of the pigment derivative (B), especially salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent, wherein the organic solvent is preferably selected from ethylene glycol, diethylene glycol, triethylene glycol, glycerol and mixtures thereof. The wording that the "mean crystallite size is in the range of from X to Y nm (or is from X to Y nm)" means: X nm ≤ number average particle size ≤ Y nm. DETAILED DESCRIPTION OF THE INVENTION The pigment preparation comprises (A) at least one organic pigment. Examples of suitable organic color pigments are: - monoazo pigments: C.I. Pigment Brown 25; - C.I. Pigment Orange 5,13, 36, 38, 64 and 67; - C.I. Pigment Red 1, 2, 3, 4, 5, 8, 9, 12, 17, 22, 23, 31, 48:1, 48:2, 48:3, 48:4, 49, 49:1, 51:1, 52:1, 52:2, 53, 53:1, 53:3, 57:1, 58:2, 58:4, 63, 112, 146, 148, 170, 175, 184, 185, 187, 191:1, 208, 210, 245, 247 and 251; - C.I. Pigment Yellow 1, 3, 62, 65, 73, 74, 97, 120, 151, 154, 168, 181, 183 and 191; - C.I. Pigment Violet 32; - disazo pigments: C.I. Pigment Orange 16, 34, 44 and 72; - C.I. Pigment Yellow 12, 13, 14, 16, 17, 81, 83, 106, 113, 126, 127, 155, 174, 176, 180 and 188; - disazo condensation pigments: C.I. Pigment Yellow 93, 95 and 128; - C.I. Pigment Red 144, 166, 214, 220, 221, 242 and 262; - C.I. Pigment Brown 23 and 41; - anthanthrone pigments: C.I. Pigment Red 168; - anthraquinone pigments: C.I. Pigment Yellow 147, 177 and 199; - C.I. Pigment Violet 31; - anthrapyrimidine pigments: C.I. Pigment Yellow 108; - quinacridone pigments: C.I. Pigment Orange 48 and 49; - C.I. Pigment Red 122, 202, 206 and 209; - C.I. Pigment Violet 19; - quinophthalone pigments: C.I. Pigment Yellow 138; - diketopyrrolopyrrole pigments: C.I. Pigment Orange 71, 73 and 81; - C.I. Pigment Red 254, 255, 264, 270 and 272; - dioxazine pigments: C.I. Pigment Violet 23 and 37; - C.I. Pigment Blue 80; - flavanthrone pigments: C.I. Pigment Yellow 24; - indanthrone pigments: C.I. Pigment Blue 60 and 64; - isoindoline pigments: C.I. Pigment Orange 61 and 69; - C.I. Pigment Red 260; - C.I. Pigment Yellow 139 and 185; BASF SE 231030 7 - isoindolinone pigments: C.I. Pigment Yellow 109, 110 and 173; - isoviolanthrone pigments: C.I. Pigment Violet 31; - metal complex pigments: C.I. Pigment Red 257; - C.I. Pigment Yellow 117, 129, 150, 153 and 177; - C.I. Pigment Green 8; - perinone pigments: C.I. Pigment Orange 43; - C.I. Pigment Red 194; - peryiene pigments: C.I. Pigment Black 31 and 32; C.I. Pigment Red 123, 149, 178, 179, 190 and 224; C.I. Pigment Violet 29; - phthalocyanine pigments: C.I. Pigment Blue 15, 15:1, 15:2, 15:3, 15:4, 15:6 and 16; - C.I. Pigment Green 7 and 36; - pyranthrone pigments: C.I. Pigment Orange 51; C.I. Pigment Red 216; - pyrazoloquinazolone pigments: C.I. Pigment Orange 67; C.I. Pigment Red 251; - thioindigo pigments: C.I. Pigment Red 88 and 181; - C.I. Pigment Violet 38; - triarylcarbonium pigments: C.I. Pigment Blue 1, 61 and 62; C.I. Pigment Green 1; - C.I. Pigment Red 81, 81:1 and 169; C.I. Pigment Violet 1, 2, 3 and 27; C.I. Pigment Black 1 (aniline black); C.I. Pigment Yellow 101 (aldazine yellow); - C.I. Pigment Brown 22. The organic pigment is preferably selected from C.I. Pigment Green 36 ( (

[0002] BASF SE 231030 8 In addition, the pigment preparation comprises (B) at least one pigment derivative selected from the group of the sulfonic acid derivatives of quinophthalone pigments. Quinophthalone derivatives especially suitable as component (B) are derived from C.I. Pigment Yellow 138 and have the following formula O YO S in which Y is selected from H, Li+, Na+, K+, wherein R1, R2, R3and R4are alkenyl; C5-C6-cycloalkyl, unsubstituted or C1-C24-alkyl-substituted; unsubstituted or C1-C24-alkyl— or C2-C24-alkenyl-substituted phenyl; unsubstituted or C1-C24-alkyl— or C2-C24-alkenyl-substituted naphthyl; a radical of the formula −[CHR6—CHR7—O]x—R5where the repeating units −[CHR6—CHR7—O] can vary for x>1; R6, R7and R5are independently hydrogen or C1-C6-alkyl; and x is an integer ≧1. BASF SE 231030 9 Y is preferably selected from H, Li+, Na+, K+, Mg2+ / 2, Ca2+ / 2 and mixtures thereof. More preferably Y is selected from H, Na+and mixtures thereof. In a particularly preferred embodiment the pigment preparation comprises (A) C. I. Pigment Green 7 and (B) a compound of formula (II), in which Y is selected from H, Li+, Na+, K+, Mg2+ / 2, Ca2+ / 2, and mixtures thereof, in particular Y is selected from H, Na+and mixtures thereof. The C. I. Pigment Green 7 particles have preferably a mean crystallite size in the range of from 22 nm to 26 nm, more preferably in the range of from 24 nm to 26 nm. The above pigment preparation is obtainable by salt kneading of C. I. Pigment Green 7 in the presence of ta compound of formula (II), in which Y is selected from H, Li+, Na+, K+, Mg2+ / 2, Ca2+ / 2, and mixtures thereof, and an organic solvent, wherein the organic solvent is selected from ethylene glycol, diethylene glycol, triethylene glycol, glycerol and mixtures thereof. The pigment preparations comprise from 0.1% to 15% by weight and especially from 0.5% to 10% by weight of component (B) based on the amounts of components (A) and (B). The pigment preparation is preferably obtainable by salt kneading or salt grinding of the organic pigment (A) in the presence of the pigment derivative (B), especially salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent. More preferably, the pigment preparation is obtainable by salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent, wherein the organic solvent is selected from ethylene glycol, diethylene glycol, triethylene glycol, glycerol and mixtures thereof. In the production process of pigment preparation, crystalline inorganic salts are used as milling salt. Use may be made of the salts or salt mixtures that are customary for salt kneading and salt grinding operations. Preference is given to sodium chloride and sodium sulfate. The weight ratio of salt to the mixture of (A) and (B) may in this case be up to 12:1 and is preferably 3:1 to 9:1. The salt kneading preferred in accordance with the invention is carried out in the presence of an organic solvent. Particularly suitable organic solvents in this context BASF SE 231030 10 include water-miscible organic solvents, especially relatively high-boiling solvents based on monomeric, oligomeric, and polymeric C2-C3alkylene glycols and their C1-C4alkyl ethers. The following may be mentioned by way of example: propylene glycol monomethyl and monoethyl ether, diethylene glycol, diethylene glycol monomethyl and monoethyl ether, triethylene glycol, triethylene glycol monomethyl and monoethyl ether, dipropylene glycol, dipropylene glycol monomethyl and monoethyl ether, and liquid polyethylene glycols and polypropylene glycols. It is appropriate to use enough solvent to give a kneadable composition. Customarily about 10 to 45 ml of solvent are needed per 100 g of salt. The salt kneading of the invention can be performed with cooling or heating at temperatures from below 0° C. to 180° C. Preferred kneading temperatures are 80 to 140° C. The kneading time is generally 1 to 24 h, particularly 2 to 5 h. Suitable kneading assemblies include, in particular, single-shaft and double-shaft kneaders and pan crushers. The kneaded material obtained can be worked up in the customary way by stirred incorporation into water, isolation by filtration, washing with water, and drying. The dried product is appropriately subjected to grinding for deagglomeration in, for example, rotor grinding or jet grinding. Alternatively the aqueous filter cake may also be freeze-dried or spray-dried. The salt grinding of the invention is preferably performed in the absence of an organic solvent. In certain cases, however, it may be advantageous to add an organic solvent in amounts of about 0.1% to 10% by weight, based on components (A) and (B). Examples that may be mentioned of suitable solvents include xylene, ethylene glycol, and dialkyl phthalates, dimethyl phthalate for example. Salt grinding can be carried out in continuous or discontinuous ball mills, vibratory mills or attritors using the customary grinding beads and / or, if appropriate, beater bars. The grinding temperatures are situated generally at room temperature to 130° C., preferably at 40 to 110° C. The grinding times should be harmonized in each case with the grinding assembly used. The grinding may take place in air but is preferably performed under inert gas. The millbase obtained can be worked up in the same way as described for the salt kneading. The security ink compositions are selected from the group consisting of low viscosity aqueous inks, low viscosity solvent-based inks, low viscosity radiation-curable inks and low viscosity dual-cure inks. Low viscosity, according to this description should define, that the viscosity of the inks should be less than about 2000 mPas, preferably less than about 1000 mPas, and even more preferably less than about 500 mPas at 1000 s-1and BASF SE 231030 11 25°C, when determined at 25°C using a rotational viscosimeter Haake Rota-Visco RV1 with a cone (DHR-2 from TA Instruments). Low viscosity aqueous (or waterborne) security inks may according to an embodiment comprise water, one or more resins, one or more wetting agents, one or more surfactants, one or more organic pigments and one or more additives. Their general composition is given in the following table: Ingredients Quantity [% by wt] Water (demineralized) 30-95 Humectants 0-30 Water-soluble or water dispersible resins 1-30 Wetting agents 0.1-10 Surfactants 0.1-10 Organic pigments 0.5-60 Other additives 0.1-10 The one or more resins may be water-soluble and / or water-dispersible resins. Water- soluble resins include for example anionic polyacrylates, polyvinyl alcohol, poly(ethylene glycol), polyvinyl pyrrolidone, polyethyleneimines, modified starch, cellulose esters or ethers (such as cellulose acetate and carboxymethyl cellulose), as well as copolymers and combinations thereof. Water-dispersible resins include for example vinyl copolymer dispersions, acrylic dispersions, polyurethanes dispersions, acrylic-polyurethane dispersions and the like. These dispersions are often referred as "latex" dispersions and the corresponding inks as latex inkjet inks. The role of the one or more resins is usually to enhance colloidal stability of the pigment particles in the ink, improve mechanical and chemical resistance properties as well as to provide adhesion of the ink layer to the substrate. The one or more wetting agents may enhance the dispersion of the organic pigment in the ink and avoid re-agglomeration and sedimentation once the pigment particles are dispersed. The one or more humectants, when present, prevent the premature drying of the inks and the clogging in particular of inkjet inks in the cartridge nozzles. Humectants include for example ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, copolymers of ethylene and propylene glycol, glycerol, trimethylolpropane, polyols, sulfonated polyethylene oxides, 2-pyrrolidone derivatives, urea derivatives, mannitol- and sorbitol-derivatives. The one or more surfactants are used, inter alia, to decrease the static surface tension of the ink, which should be lower than about 40 mN / m, preferably lower than about 35 mN / m, more preferably lower than about 30 mN / m and even more preferably lower BASF SE 231030 12 than 25 mN / m in order to ensure a good wetting of the substrate. The static surface tension is measured using a force tensiometer equipped with a Wilhelmy plate. The one or more additives may include preservatives, anti-foaming agents, fillers (such as pyrogenic silica), pH-control agents. They also may include forensic markers and / or taggants. The density of the ink vehicle (i.e. all components of the ink except the one or more organic pigments) is essentially depending on the amount of water contained in the ink, i.e. it is between about 1000kg / m3and about 1100kg / m3. Once printed, for example by ink jetting, on a desired substrate and / or medium, the water contained in the ink is partially absorbed by the substrate or medium, respectively, and partially evaporated using a hot air tunnel and / or infrared heaters. Since at least a part of the ink vehicle (water) has to be absorbed by the substrate, said substrate is preferably chosen from the group consisting of substrates made of porous materials and substrates comprising a dedicated ink-receptive layer. Substrates made of porous materials typically include paper or other fibrous materials (including woven and non-woven fibrous materials), as well as composite materials. Typical paper, paper-like or other fibrous materials are made from a variety of fibers including without limitation abaca, cotton, linen, wood pulp, and blends thereof. As is well known to those skilled in the art, cotton and cotton / linen blends are preferred for banknotes, while wood pulp is commonly used in non-banknote security documents. Typical examples of composite materials include multilayer structures or laminates made of at least one bottom plastic or polymer layer and at least one top paper layer (such as Durasafe® from Landqart, which features a polyamide layer sandwiched between two cotton paper layers), as well as plastic and / or polymer fibers incorporated in a paper-like or fibrous material such as those described here above. Substrates comprising a dedicated ink-receptive layer are made of at least one bottom layer made of either porous or non-porous materials, or a blend or combination thereof, and at least one top layer comprising porous materials. If the at least one bottom layer is made of porous materials, said porous materials are the same as described here above. If it is made of non-porous materials, said non-porous materials include glasses, metals, ceramics, plastics and polymers, metallized plastics or polymers. Typical examples of plastics and polymers include polyolefins such as polyethylene (PE) and polypropylene (PP) including biaxially oriented polypropylene (BOPP), polyamides, polyesters such as poly(ethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), poly(ethylene 2,6-naphthoate) (PEN) and polyvinylchlorides (PVC). Spunbond olefin fibers such as those sold under the trademark Tyvek® may BASF SE 231030 13 also be used as substrate. Typical examples of metalized plastics or polymers include the plastic or polymer materials described hereabove having a metal disposed continuously or discontinuously on their surface. Typical example of metals include without limitation aluminum (Al), chromium (Cr), copper (Cu), gold (Au), silver (Ag), alloys thereof and combinations of two or more of the aforementioned metals. The metallization of the plastic or polymer materials described hereabove may be done by an electrodeposition process, a high-vacuum coating process or by a sputtering process. The top ink-receptive layer contains either porous particles aimed at absorbing the water contained in the ink, one or more binders, and optional additives, or polymers that absorb water and swell upon impact of ink drops. Porous particles include metal oxides such as aluminum oxide (such as v- alumina), aluminum oxide / hydroxide (such as pseudo-boehmite), titanium dioxide (rutile or anatase), zinc oxide or silica (fumed or precipitated), carbonates (such as calcium carbonate or sodium aluminium carbonate), silicates (e.g. magnesium silicate, aluminum silicate), sulfates (such as barium sulphate) and combinations thereof. If transparency of the ink-receptive layer is mandatory, the use of porous particles made of a material with low refraction index and small particle size (such as fumed silica or pseudo-boehmite) is preferable. The one or more binders include gelatin, polyvinyl alcohol, derivatives of polyvinyl alcohol, polyvinyl pyrrolidone and mixtures thereof. The amount of binder is between about 5 wt-% and about 100 wt-% of the amount of porous particles, preferably between about 10 wt-% and 50 wt-%, and more preferably between about 15 wt-% and about 30 wt-%. One of the additives known to someone skilled in the art is boric acid, that acts as an efficient crosslinker for the above- mentioned polymers. Polymers that swell with water include for example polyvinyl alcohol, modified polyvinyl alcohol, gelatine, starch, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, methoxyethyl cellulose, gum arabic, polyvinyl pyrrolidone, polyvinyl-methyl pyrrolidone, polyacrylic acid, polyacryl amide, cationic polymers such as quaternised polyvinyl pyridine, and combinations thereof. Swelling helps fixing the ink dots and avoiding ink run-off. Water then slowly evaporates (eventually aided by passing the printed substrate into a hot air tunnel) and the layer thickness gets back to its nominal value (i.e. its value before printing). Substrates specifically produced for inkjet printing are usually composite substrates that possess at least a core of paper or paper-like material, and two layers of non-absorbing polymer (such as polyethylene or PET) on both sides of the paper core. The ink-absorptive layer has described hereabove may be present on one or both sides of the substrate. Additionally, and in certain cases, a primer layer may be present between the one or more bottom layers and the ink-receptive layer, in order to enhance adhesion. BASF SE 231030 14 Alternatively, the one or more bottom layers may be treated by electrostatic discharge (corona) before coating or printing of the ink-receptive layer for the same purpose. Low viscosity solvent-based security inks preferably comprise one or more organic solvents, one or more resins (or resins), one or more wetting agents, one or more organic pigments and one or more additives. Their general composition is given in the following table: Ingredients Quantity [% by wt] Organic solvents 30-95 Resins 1-30 Wetting agents 0.1-10 Surfactants 0.1-10 Organic pigments 0.5-60 Other additives 0.1-10 The one or more solvents used according to this preferred embodiment of the invention include for example alcohols (such as ethanol), ketones (such as methyl ethyl ketone), esters (such as ethyl acetate or propyl acetate), glycol ethers (such as DOWANOL DPM) or glycol ether esters such as butyl glycol acetate and the like. The one or more resins for solvent-based inks include for example nitrocellulose, methyl cellulose, ethyl cellulose, cellulose acetate, polyvinylbutyrals, polyurethanes, polyacrylates, polyamides, polyesters, polyvinyl acetate, rosin modified phenolic resins, phenolic resins, maleic resins, styrene- acrylic resins, polyketone resins, vinylic resins, and the like. The one or more wetting agents are used to preferably stabilize the pigment particles in the ink and to increase the interaction between the pigment particles and the resin matrix once the one or more solvents have evaporated. After printing, such as for example, ink jet printing, the printed substrate might further be conveyed to a hot air and / or an infrared tunnel and the one or more solvents are evaporated by passing through this tunnel. Simultaneously with the evaporation of the one or more solvents, the thickness of the printed layer shrinks and the polymers contained in the one or more resins begin to harden, leading to a strong increase of viscosity that allows safe handling of the printed substrate ("dry-to-touch" state). The one or more additives may include preservatives, levelling agents, plasticizers and fillers (such as pyrogenic silica). They also may include forensic markers and / or taggants. The density of the ink vehicle (i.e. all components of the ink except the one or more pigments) is essentially depending on the solvents contained in the ink, i.e. it is usually between about 800kg / m3and about 1100kg / m3. BASF SE 231030 15 As for the low viscosity aqueous inks, the static surface tension of the low viscosity solvent-based inks should be lower than about 40 mN / m, preferably lower than about 35 mN / m, more preferably lower than about 30 mN / m and even more preferably lower than 25 mN / m in order to ensure a good wetting of the substrate and a good drop formation upon ink jetting. Since drying of solvent-based inks is usually mainly obtained through evaporation of the one or more solvents, non-porous as well as porous substrates as discussed previously for the low viscosity aqueous inks may be used with solvent-based inks. In certain cases, a specific ink-receptive layer may be present. Alternatively, the substrate may be treated by electrostatic discharge (corona) before printing to enhance adhesion between the dried ink layer and said substrate. Low viscosity radiation-curable inks, preferably security inks, suitable which may be used according to yet another embodiment of the invention preferably comprise one or more radiation-curable monomers, one or more radiation-curable oligomers, one or more photoinitiators, one or more wetting agents, one or more security pigments and one or more additives. Their general composition is given in the following table: Ingredients Quantity [% by wt] Monomers 20-90 Oligomers / prepolymers 0-70 Photoinitiators 1-15 Wetting agents 0.1-10 Organic pigments 0.5-60 Other additives 0.1-10 The one or more monomers and the one or more oligomers / pre-polymers used in the ink composition are polymerized to be solidified by the function of the one or more photoinitiators when being submitted to radiation, and are not otherwise limited. For example, various monomers and oligomers having a monofunctional group, a bifunctional group, or a trifunctional or more polyfunctional group can be used. Polymerization may be performed by electron beam (EB)-curing or UV-curing. Preferably, polymerization is performed by UV- curing with LED (light-emitting diodes) and the one or more photoinitiators are chosen accordingly. The number of LEDs is not limited to one, and a plurality of LEDs may be used so as to emit light having a plurality of emission peak wavelengths. The one or more additives may include one or more sensitizers, one or more polymerization inhibitors, one or more surfactants, as well as preservatives, levelling agents, plasticizers, fillers (such as pyrogenic silica) and standard color-imparting pigments. They also may include forensic markers and / or taggants. BASF SE 231030 16 The density of the ink vehicle (i.e. all components of the ink except the one or more pigments) is essentially depending on the mixture of monomers / oligomers present in the ink. It is usually comprised between about 1100 kg / m3and about 1300 kg / m3. The advantages of radiation-curing inks are that drying is usually almost instantaneous and no volatile components are released. As in the case of solvent-based inks, any type of substrate (porous or non- porous) may be used with radiation-curable inks without limitation. The substrate may be treated by electrostatic discharge (corona) before printing to enhance adhesion between the cured ink layer and said substrate. Low viscosity dual-cure inks, preferably security inks, according to yet another embodiment of the invention comprise preferably the same ingredients as radiation- curing inks, and one or more solvents. Ingredients Quantity [% by wt] Solvents 5-50 Monomers 5-70 Oligomers 0-50 Photoinitiators 2-15 Wetting agents 0.1-5 Organic pigments 0.5-60 Other additives 0.1-10 The one or more solvents are usually evaporated by conveying the printed substrate to a hot air tunnel and / or infrared heaters, then the radiation-curing part of the ink is cured, preferably by UV curing using UV-LEDs. The density of the ink vehicle (i.e. all components of the ink except the one or more pigments) is essentially depending on the mixture of monomers / oligomers and on the solvents present in the ink. It is usually comprised between about 900kg / m3and about 1100kg / m3. As in the case of low viscosity solvent-based inks and low viscosity radiation-curable inks, any type of substrate / medium (porous or non-porous) may be used with low viscosity dual-cure inks without limitation. The substrate may be treated by electrostatic discharge (corona) before printing to enhance adhesion between the cured ink layer and said substrate. The security ink compositions of the present invention are preferably applied by inkjet printing and can be used in the production of security documents. Accordingly, the present invention relates to a process for the manufacture of a security document comprising the steps applying on a substrate the low viscosity security ink according to the present invention; and to a security document, comprising a substrate BASF SE 231030 17 and the pigment preparation of the present invention, or obtainable by the above process. The term "security document" refers to a document which is usually protected against counterfeit or fraud by at least one security feature. The term "security feature" is used to denote an image, pattern or graphic element that can be used for authentication purposes. The security document is preferably selected from a banknote, a passport, a check, a voucher, an ID- or transaction card, a stamp and a tax label, especially banknotes. Various features and aspects of the present invention are illustrated further in the examples that follow. While these examples are presented to show one skilled in the art how to operate within the scope of this invention, they are not to serve as a limitation on the scope of the invention where such scope is only defined in the claims. Unless otherwise indicated in the following examples and elsewhere in the specification and claims, all parts and percentages are by weight, temperatures are in degrees centigrade and pressures are at or near atmospheric. Examples Mean Crystallite Size Powder X-ray diffraction (PXRD) data was collected using a diffractometer (D8 Advance Series II, Bruker AXS GmbH) equipped with a LYNXEYE detector operated with a Copper anode X-ray tube running at 40kV and 40mA and the geometry was Bragg- Brentano. The diffraction reflections of the X-ray powder diffraction diffractogram are mathematically fitted using the modelling software DIFFRAC.TOPAS provided by Bruker AXS GmbH and the full widths at half maximum (FWHM) of the diffraction reflections are determined. The crystallite size is determined using the Scherrer equation in the range of 4.5oto 17oreflections and the mean crystallite size is calculated. As is known to a person skilled in the art, the Scherrer equation is as follows: d=(K*λ) / (β*cos θ), where d is the crystallite size, K is a dimensionless shape factor, λ is the wavelength of the X-radiation, β is the full width at half maximum of the reflection, measured in radians, θ is the diffraction angle. A value of 0.94 was taken for K. BASF SE 231030 18 Example 1 Production of Inventive Pigment Preparations The following designations are used in the examples: Pigment (A1): C.I. Pigment Green 7, prepared in a similar way as described in example 1 of US 2009 / 0121201A1 (mean crystallite size: 31.01 nm). Pigment Derivative (B1): pigment derivative of formula lI defined above, wherein Y is H / Na, prepared as per example 1 of WO02 / 00643. A mixture of 1050 g of pigment (A1), 52.2 g of pigment derivative (B1), 5800 g of sodium chloride and 950 g of triethylene glycol is kneaded in a 10-l high-speed kneader (Turbulent High-Speed Kneader TR 10 from Drais) at 90° C (temperature of the kneaded composition) for 2 h. The kneaded material obtained is stirred up in water, isolated by filtration and washed salt-free with water, then dried in a forced-air cabinet at 70° C and ground using a rotor mill. The mean crystallite size of the obtained pigment preparation is 25.03 nm). Preparation of a continuous inkjet (CIJ) ink A pigment paste using the pigment of Example 1 was prepared by mixing the components of Table 1A. The paste was milled using a bead milling DISPERMAT® CA (from VMA-Getzmann GMBH) (beads of 1 mm diameter; 200 g of beads / 100 g of paste; milling for 30 minutes at 5000 rpm). The beads were washed with 25 ml methyl ethyl ketone (MEK) to recover the paste. The resulting pigment paste (comprising the MEK used to wash the beads) was used to prepare a CIJ ink disclosed in Table 1B by mixing the pigment paste with the other components using a DISPERMAT® CA (VMA- Getzmann GMBH) equipped with a disc-shaped stirrer; mixing for 15 minutes at 2000 rpm). Table 1A: Pigment paste Components wt% VINNOL E15 / 40A (vinyl chloride copolymer from Wacker 9.5 Chemie) (CAS Nr 53710-52-4) DYSPERBYK 108 (from BYK) (CAS Nr 67784-78-5) 0.45 Methyl ethyl ketone (CAS Nr 78-93-3) 59 Pigment from Example 1 10 Table 1B: CIJ ink Components wt% VINNOL E15 / 40A (vinyl chloride copolymer from Wacker 4.35 Chemie) (CAS Nr 53710-52-4) ETHOCEL™ Standard 100 (ethyl cellulose) (from Dupont) 0.5 (CAS Nr 9004-57-3) BASF SE 231030 19 DYSPERBYK 108 (from BYK) (CAS Nr 67784-78-5) 0.45 Lithium perchlorate (Sigma Aldrich) (CAS Nr 7791-03-9) 0.5 Methyl ethyl ketone (CAS Nr 78-93-3) 91.2 Pigment from Example 1 3 Viscosity 3 mPa.s Sedimentation test A sedimentation test was run with the ink of Table 1 using a TURBISCAN (from MICROTRAC; equipped with an 880 nm diode and two synchronous optical sensors for measurement of the transmitted light (at 180° from the incident light) and measurement of the backscattered light (at 45° from the incident light). The sedimentation test was measured as the backscattered light percentage (R(%)) and its evolution over time. The percentage of backscattered light refers to the light input and is a measure of the backscattered light at 45° as compared to the illumination light. No transmission was observed, that is T(%) was 0. The difference between 100% and the R(%) resulted from backscattered light not captured by the optical sensor at 45°. A glass cell was filled with a freshly prepared sample of the CIJ ink (20 ml) of Table 1B. Measurements of the backscattered light at a height of 1.2 cm from the bottom of the glass were done immediately after the ink preparation (t0), 3 days (t1) and 30 days (t2) after the ink preparation (glass cell containing the ink stored at room temperature). The stability of the CIJ ink was assessed as sufficient as R(%) variation between (t0) and (t1) was only 4%, and only 12% between (t0) and (t2).

Claims

BASF SE 231030 20 Claims 1. Use of a pigment preparation for security applications, or in low viscosity security inks, wherein said pigment preparation comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophthalone pigments; wherein the organic pigment (A) particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm, wherein the low viscosity security inks are selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks.

2. Use of the pigment preparation according to claim 1, wherein the pigment ,3. Use of the pigment preparation according to claim 1, or 2, wherein the organic pigment is selected from C.I. Pigment Green 36 ( ),BASF SE 231030 214. Use of the pigment preparation according to any of claims 1 to 3, wherein the pigment preparation comprises (A) C. I. Pigment Green 7 and (B) a compound of formula (II).

5. Use of the pigment preparation according to claim 4, wherein the C. I. Pigment Green 7 particles have a mean crystallite size in the range of from 22 nm to 26 nm, especially in the range of from 24 nm to 26 nm.

6. Use of the pigment preparation according to any of claims 1 to 5, wherein the pigment preparation is obtainable by salt kneading or salt grinding of the organic pigment (A) in the presence of the pigment derivative (B), especially salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent.BASF SE 231030 22 7. Use of the pigment preparation according to claim 4, wherein the pigment preparation is obtainable by salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent, wherein the organic solvent is selected from ethylene glycol, diethylene glycol, triethylene glycol, glycerol and mixtures thereof.

8. A low viscosity security ink selected from the group of screen printing inks, flexography printing inks, heliogravure printing inks, staining inks, inkjet printing inks, spray coating inks, aerosol jet printing inks, electrohydrodynamic printing inks, slot die coating inks, and Laser Induced Forward Transfer (LIFT) printing inks, comprising a pigment preparation, which comprises (A) at least one organic pigment, (B) at least one pigment derivative, selected from the group of the sulfonic acid derivatives of quinophthalone pigments; wherein the organic pigment particles have a mean crystallite size in the range of from 15 nm to 28 nm, especially in the range of from 20 nm to 28 nm.

9. The ink according to claim 8, wherein the pigment derivative is a compound ofC.I. Pigment Green 36 ( PigmentBASF SE 231030 23 11.comprises (A) C. I. Pigment Green 7 and (B) a compound of formula (II).

12. The ink according to claim 11, wherein the C. I. Pigment Green 7 particles have a mean crystallite size in the range of from 22 nm to 26 nm, especially in the range of from 24 nm to 26 nm.

13. The ink according to any of claims 8 to 12, wherein the pigment preparation is obtainable by salt kneading or salt grinding of the organic pigment (A) in the presence of the pigment derivative (B), especially salt kneading of the organic pigment (A) in the presence of the pigment derivative (B) and an organic solvent.

14. A process for the manufacture of a security document comprising the steps applying on a substrate the low viscosity security ink according to any of claims 8 to 13.BASF SE 231030 24 15. A security document, comprising a substrate and the pigment preparation defined in any of claims 1 to 7, or obtainable by the process according to claim 14.

16. The security document according to claim 15, which is selected from a bank note, a passport, a check, a voucher, an ID- or transaction card, a stamp and a tax label.

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