IR-absorbing intaglio ink

REPUBLIC

POLAND (12) TRANSLATION OF THE EUROPEAN PATENT (19) PL (11) PL / EP 1790701

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(13) T3

Patent Office of the Republic of Poland (96) Date and number of the European patent application:

November 25, 2005 05111295.1 (97) The grant of the European patent was announced: January 7, 2009 European Patent Bulletin 2009/02 EP 1790701 B1 (51) Int. Cl.

C09D11 / 02 B41M3 / 14 (2006.01) (2006.01) (54) Title of the invention:

Infrared absorbing gravure printing ink (30) Priority:

(43) Application was announced:

30.05.2007 European Patent Bulletin 2007/22 (45) The following was announced about the submission of the translation of the patent:

30.06.2009 News of the Patent Office 06/2009 (73) Authorized by the patent:

SICPA HOLDING SA, Prilly, CH (72) Inventor (s):

Demartln Maeder Marlyse, La Sarraz, CH

O Muller Edgar, Frlbourg, CH

I— Despland Claude Alain, Prilly, CH

Degott Pierre, Crissier, CH τΟ

O (74) Agent:

ABOUT

Przedsiębiorstwo Rzeczników Patentowych Patpol Sp. z o. o

thing, pat. Kiciak Krzysztof_n 02-770 Warszawa 130 n P.O. Box. 37

ABOUT.

Attention:

Within nine months of the publication of the information on the grant of the European patent, any person may file an objection to the European Patent Office against the European patent granted. The objection must be submitted in the form of a written statement of reasons. It is considered brought only when the opposition fee has been paid (Art. 99 (1) of the Convention on the Grant of European Patents).

ΕΡ 1 790 701 Β1

[0001] The present invention is in the field of inks and coating compositions. In particular, it relates to an ink for a printing process with an engraved steel matrix (copperplate, gravure) which is used to print banknotes and other security materials. More specifically, the gravure ink of the present invention is designed to selectively absorb radiation in parts of the "optical infrared" spectrum, while being transparent in other parts of it.

[0002] Compounds and coatings which absorb radiation in the "optical infrared" range of the electromagnetic spectrum, ie between 700 nm and 2500 nm wavelength, are known to the skilled person. Such materials are used as solar energy absorbers as well as for the production of invisible, automatically readable signs on objects or documents, for the automated processing or authentication of objects or documents by devices.

[0003] Throughout this specification, the expressions "infrared" or "IR" are used to denote the spectral range between 700 nm and 2500 nm. The term "visible" is intended to describe the spectral range between 400 nm and 700 nm. The term "ultraviolet" or "UV" should be used for wavelengths less than 400 nm. In addition, the terms "near infrared" or "NIR" are used to denote the spectral range between 700 nm and 1100 nm wavelength, which corresponds to radiation detectable by conventional silicon photodetectors.

[0004] Throughout the description, the terms engraved steel die printing process, copperplate printing process and gravure printing process are used synonymously to denote the same printing technique.

[0005] The first group of prior patents for infrared-related printing techniques relates only to processing aspects: US 3 705 043 (Zabiak) discloses an infrared-absorbing (IR-absorbing) inkjet ink composition for printing auto-read barcodes. At the time of this disclosure (1972), barcode reading equipment, for technical reasons, was associated with the "near infrared" spectrum range (700 nm - 1100 nm); for this reason, an infrared absorbing organic dye nigrosine was added to the paint so that it was also "visible through the device". A similar technical purpose has been sought in US Patents 3,870,528 (Edds et al., IBM) and US 4,244,741 (Kruse, US Form Service); the latter discloses the use of reduced heteropoly (phosphomolybdic) acid as an inorganic infrared absorbent. It can be concluded that these publications do not address the use of IR-absorbing substances as security markings.

[0006] A second group of publications relates to security materials: EP-A-0 552 047 (Nishida et al., Hitachi Maxell Ltd.) discloses a security material containing a printed infrared-absorbing mark having a colored cover layer to hide the IR-absorbing element. protecting in the visible spectral range of 400 nm - 700 nm. IR absorbers according to the teachings of EP-A-0 552 047 must be used in conjunction with cover layers which mask their existence and position from the naked eye. In EP-A-0 263 446 (Abe et al., Dainichiseika Color &amp; Chemicals Mfg. Co. Ltd.) discloses an anti-copy print containing latent information on a security material as well as a method for producing said print wherein an IR absorbing black ink is used in addition to and in combination with IR transparent standard four color process inks. An "IR-absorbing black" is preferably a carbon black which absorbs freely throughout the visible and infrared spectral ranges, while an "IR-transparent black" is an organic dye that absorbs only in the visible and infrared spectral range.

[0007] In the field of automatic banknote handling, IR absorption plays an important role. Most of the money circulating today contains not only visible color imprints, but also specific features that are only detectable in the infrared part of the spectrum. Generally, these IR features are placed for use in automatic money handling equipment, banking and sales applications (ATMs, vending machines, etc.) to recognize a particular banknote and verify its authenticity, in particular to distinguish it from copies from color copiers. WO-A-04/016442 (Banque de France) relates to documents secured with an infrared absorbing material.

The visible appearance (black) of the infrared absorbing paints according to EP-A-0 263 446 is seen as a drawback in security applications where IR-absorption should be used as an additional, hidden, ie invisible, feature. This difficulty can be overcome by disguising the IR absorbing ink by overprinting, or by using IR absorbing and IR transparent inks having the same visible color; however, this option imposes a rather demanding restriction on the document designer because it is not compatible with transparent shades.

[0009] Another group of patents discloses invisible IR absorbents that can be used in paints of all shades (including white) without affecting their visible appearance: EP-A-0 608 118 (Yoshinaga et al., Canon KK) discloses a means (such as a banknote, security material, etc.) described with invisible information as an automatic recognition method for security material to prevent its being copied by copiers.

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[0010] The recording is made using near infrared-absorbing organic cyanine substances which are colorless and transparent in the visible part of the spectrum and therefore invisible to the human eye. A similar approach was taken by Tashima et al., Dainippon Printing Co. Ltd., disclosing the use of inorganic ytterbium phosphate (YbPO₄) as an invisible IR absorbing security element, as well as suitable inks and coating compositions containing it, including security materials and patterns that can be made with it (JP 08-143853 A2; JP 08-209110 A2; JP 09- 030104 A2; JP 09-031382 A2; JP 09-077507 A2; JP 09-104857 A2; JP 10-060409 A2). Finally, US 5,911,921 (Takai et al; Shin-Etsu Chemical Co., Ltd.) discloses non-stoichiometric ytterbium phosphate with an even lower IR reflectance for use as an IR-absorbing security material.

[0011] The organic and inorganic IR absorbers of the latter group of documents thus overcome the drawbacks of visible coloring of the IR absorber; however, there is another drawback associated with their use, that is, the fairly narrow spectral width of the infrared absorption bands exhibited by organic cyanine type dyes and YbPO IR absorbent₄. It should be noted that the detection (reading) of features with a narrow IR absorption band requires specially adapted detection equipment to read the exact absorption wavelength given, and in the case of YbPO₄, using a relatively high concentration of IR-absorbing material in the printing ink.

[0012] There are many different models of money handling equipment on the market today, from many vendors around the world. This equipment, although it allows checking banknotes for IR absorption, does not work on one and the same IR wavelength; An "IR color standard" analogous to the CIELAB standard used in visible colorimetry does not actually exist.

[0013] Narrow band IR absorbers are therefore not compatible with general money handling applications due to incompatibility with already existing handling equipment. It should be noted that it is usually not possible to adapt existing money handling equipment in banking and auto sales after each change to a new type of IR absorbing security element.

[0014] On the other hand, the classic option of using carbon black as an unrestricted broadband IR absorber has the already mentioned drawback of limiting the designer of the banknote to shades of gray or black. There is also the general availability of this type of material; thus, carbon black, although it is an IR absorbent, cannot be considered a containment material. The same applies to semi-metallic graphite, the use of which as an IR-absorbing pigment for security materials has been disclosed by Murl in WO-A-98/28374.

[0015] In the best embodiment, the IR absorber in money handling applications should be transparent in the visible range (400 nm to 700 nm) to allow its use in all types of visibly colored inks as well as in markings that are invisible to the naked. the eye and show strong absorption in the near infrared range (700 nm to 1100 nm), to enable easy recognition by standard money handling equipment (based on silicone IR photodetectors which are sensitive up to 1100 nm). The IR absorbent should furthermore be transparent again somewhere in the range 1100nm to 2500nm to distinguish this particular money-saving feature from being printed with plain carbon black or graphite, which absorb without limitation over the entire IR range. Such a distinction can be made e.g. by simply checking the transparency in the region 1100-2500 nm, using a suitable photocell (Ge, InGaAs, etc.).

[0016] Steel die printing (copperplate printing, gravure printing) is a fairly specific method of producing money and other highly secured state-issued documents. Gravure printing presses are heavy and expensive equipment that is otherwise not available for industrial printing applications and that is only used by the few high security printing houses in the world. Consequently, even a security feature with a moderate degree of technical level can be used with a high security level if applied by a gravure printing process. The state of the art relating to inks for the steel die printing process is given in EP-A-0 340 163; EP-A-0 432 093; US 4,966,628; US 5,658,964; as well as WO 02/094952 of the applicant; the content of these documents is attached by reference.

[0017] The gravure inks for printing security features are characterized by a pasty consistency (having a fairly high viscosity value of more than 3, preferably more than 5 Pascal seconds (Pa s) at 40 ° C) and in particular a high solids content, typically more than 50% by weight. Security materials, such as banknotes, must also be durable and resistant to sunlight and environmental influences (i.e. humidity, oxygen, washing and common solvents and chemicals). Particularly well-resistant ink formulations containing high-performance epoxy ester or urethane binder resins are therefore used for printing such documents. Pigments, fillers and other solids contained in the gravure printing ink are advantageous for the same reason

EP 1 790 701 nie1 with inorganic compounds; however, organic pigments showing high resistance can also be used.

[0018] The object of the present invention is an intaglio printing ink meeting the above requirements.

[0019] It has now surprisingly been found that the above problem is solved by an ink for an engraved steel die printing process, the ink containing a polymeric organic binder, an infrared absorber, and, if desired, a solvent and / or filler, and the ink has a pasty consistency of a viscosity of at least 3, preferably 5 Pa s at 40 ° C, and wherein the infrared absorbing material comprises transition element atoms or ions, the infrared absorption of which is the result of electron transitions in the d-shell of transition element atoms or ions.

[0020] A class of substances has been unexpectedly discovered that are suitable as broadband IR absorbents in gravure printing inks, meeting the requirements and overcoming the drawbacks of both narrow band IR absorbents and unlimited carbon black or graphite IR absorbents. Such infrared-absorbing substances, which may be organic or inorganic in nature, are characterized by containing specific chemical elements having an incomplete d-electron shell (i.e. transition element atoms or ions), the infrared absorption of which is a consequence of electronic transitions in this d-shell of an atom or ion. It turned out that selected compounds of the appropriate transition element atoms or ions absorb in the NIR range (700 nm to 1100 nm), and are almost transparent in the visible range (400 nm to 700 nm) of the spectrum, as well as in a certain range between 1100 nm and 2500 nm. These materials, despite the fact that they only show moderately strong absorption in this NIR range, can be applied by gravure printing such that a sufficient amount of IR-absorbing material is transferred to the security material to obtain a useful IR contrast (absorption density).

[0021] Electronic dd transitions taking place in the incomplete d-shell of a transition element atom or ion are known to a person skilled in the art of inorganic spectroscopy. In this context, mention may be made of ABP Lever, "Inorganic Electronic Spectroscopy, ed. 2, "Studies in Physical and Theoretical Chemistry, vol. 33, Elsevier, Amsterdam, 1984, chapter 6. The terms "transition element" or "transition metal" should in the context of the present invention refer to the sequence of the chemical elements 22 (Ti) through 29 (Cu), 40 (Zr) through 47 (Ag), and 72 (Hf) through 79 (Au) of the periodic table, with particular emphasis on the first transitional series (Ti, V, Cr, Mn, Fe, Co, Ni, Cu).

Preferably, the transition element in the infrared-absorbing compound is present in the form of an ion such as titanium (III), vanadium (IV) = vanadyl, chromium (V), iron (II), nickel (II), cobalt (II) ions. or copper (II) (corresponding to the chemical formula Ti³⁺, VO, Cr⁵⁺, Fe²⁺, Ni²⁺, What²⁺, and Cu²⁺). Moreover, more than one transition element atom or ion, as well as other atoms or ions (cations or anions), may be present in the compound for structural reasons or for the purpose of achieving a cumulative effect.

[0023] Substances in which the light absorption is a consequence of electronic transitions in the d-shell of transition element atoms or ions exhibit a simply moderate specific absorption. The lack of proper light absorption therefore has to be compensated for by a sufficiently large amount of substance, i.e. a sufficiently thick layer of substance must be present to obtain the desired absorption properties. The IR-absorbing substances of the prior art based on the transition in the d coating have therefore been used in a thick coating layer (IR absorbing solar panel paints), or used as fillers in a bulk plastic material.

[0024] D-coated transition elements based infrared absorbers have not, however, been used in common printing applications where the available layer thickness varies from just a few micrometers in offset and flexographic printing, up to 10 to 15 micrometers dry residue in screen printing applications, however. and wherein only part of the total layer thickness is the pigment charge. Given these limitations, one skilled in the art of paint formulation prefers to use an IR-absorbing material that exhibits high specific infrared absorption to obtain the desired result with a reduced amount of material.

[0025] It has been found that using the gravure printing process it is possible to transfer a fairly thick layer (up to 50 microns) of high solids ink to the substrate. Thus, by using a gravure printing process, a sufficient amount of coating-based IR-absorbing substances can be applied to the document to obtain a useful infrared contrast. Moreover, the disclosed IR-absorbing substances are not commonly available in printing applications, which makes them suitable for security printing applications due to the lack of readily available counterfeit possibilities.

[0026] The infrared absorption properties of transition element compounds are known and already used in certain areas of the art. Iron (II) and copper (II) compounds containing Fe (²⁺) or Cu (²⁺) in a suitable chemical environment, have proved to be effective substances to absorb a wide IR band in the near infrared range. Suitable iron (II) or copper (II) compounds are transparent in the visible range of the spectrum - exhibiting at most a slightly yellowish or bluish tinge - and persistent in ordinary

ΕΡ 1 790 701 Β1 environmental conditions (ie, exposure to oxygen and moisture). A "suitable chemical environment" is, for example, a phosphate or a polyphosphate ion, or, more generally, a group containing phosphorus and oxygen; in many of the disclosed IR-absorbing substances of the prior art, the Cu ion (²⁺) or Fe (²⁺) is in fact bonded via an oxygen atom to a phosphorus atom to form the sequence of MOP atoms.

[0027] US 4,296,214 (Kamada et al., Mitsubishi Rayon Co., Ltd.) discloses a sunlight-absorbing acrylic resin having copolymerized copper (II) acrylic diphosphonate esters. US 5,466,755 (Sakagami et al., Kureha Kagaku Kogyo KK) discloses an optical plastic filter material based on an acrylic copolymer containing monohydrophosphate diester and dihydrogenphosphate monoester groups into which copper (II) and / or iron (II) ions have been incorporated ( ll). US 6,410,613 (Ohnishi et al., Kureha Kagaku Kogyo KK) discloses further IR absorbing phosphate ester polymers containing copper ions. These polymeric materials are useful as near infrared absorbers (filters) in the wavelength range from 700 nm to 1200 nm, but they have not been used in printing inks to date.

[0028] US 5,236,633 and US 5,354,514 (Satake et al., Jujo Paper Co., Ltd.) describe a near infrared absorbent material based on a transparent thermoplastic polymer (polymethacrylate, polycarbonate, polyethylene, vinyl chloride, etc.) ), an organic thiourea compound, and a copper compound that fuse together to form a visible (slightly blue) transparent, IR-absorbing plastic. US 5,723,075 (Hayasaka, Nippon Paper Industries, Co., Ltd.) discloses a similar technique, except that dimerized organic thiourea derivatives are used.

[0029] US patents US 2,265,437 and US 5,800,861, issued to The Sherwin-Williams Company, disclose the use of, inter alia, copper phosphate, basic copper phosphate, and copper pyrophosphate in IR absorbing coatings for making passive solar collectors and the like. . Such coatings are characterized by having, in addition to the absorption in the visible spectrum, a broad absorption band in the region of 700 nm to 1200 nm.

[0030] Glasses containing phosphate and / or fluoride, including copper ions (²⁺) have also been used as IR absorbers, in particular for IR cut-off filters in the optical industry. US 5,173,212 (Speit et al., Schott Glaswerke) and US 2004/0082460 (Yamane et al., HOYA Corporation) disclose corresponding glass formulas and the resulting light absorption spectra.

[0031] JP 05-279078 A2 (Manabe et al., Asahi Glass Co. Ltd.) discloses a near infrared absorbing material for use in screen printing which is a colorless copper (II) glass powder with phosphoric acid mixed with a substance resin, used for automatic information reading in near-infrared laser light. In JP 06-207161 A2 (Usui et al., Asahi Glass Co. Ltd.) discloses another screen printing ink which contains copper (II) phosphates as a semiconductor laser light absorber (810 nm). JP 05-093160 A2 (Matsudaira, Toppan Printing Co. Ltd.) discloses a two component screen printing ink for printing invisible secret information. The paint contains, as the IR-absorber, a powdered phosphate glass containing iron (II) and / or copper (II) oxide (from Asahi Glass Co. Ltd.). JP 06-107985 A2 (Matsudaira et al., Toppan Printing Co. Ltd.) discloses a further two-component IR-absorbing ink based on glassy white copper (II) and / or copper / iron (II) phosphates as IR absorbers. Such inks are used to print auto-read barcodes on security materials such as long-term plastic credit cards, ID cards, etc., where the printed information must be read by a semiconductor near infrared laser. Printing inks for engraved steel dies (copperplate, gravure) containing these classes of near infrared absorbing compounds including copper (II) or other transition element atoms or ions have not been disclosed to date.

[0032] The ink according to the present invention, for the engraving steel die printing process, comprises an organic binder, a resin, preferably a high resistance epoxy ester, urethane alkyd or a UV-curable resin, as well as an infrared absorber according to the invention, optionally one or more pigments forming the desired visible color, optionally fillers and / or a solvent to bring the paint viscosity to a value above 3 Pa s, preferably above 5 Pa s at 40 ° C, and optionally further additives such as drying agents, photoinitiators, waxes and rheology additives. An infrared absorber is a transition element compound whose IR absorption is due to electronic transitions in the d-shell of transition element atoms or ions. Gravure printing inks formulations and materials normally used in the manufacture of gravure printing inks (i.e. binders, fillers, solvents, pigments and other paint additives) are known to those skilled in the art and need not be discussed further here.

[0033] The source of IR absorption in the gravure printing inks disclosed herein is different from the IR absorbent YbPO.₄disclosed by Tashima et al. (e.g. JP 08-143853), which is a source with a narrow absorption band and caused by an electron transition in the f shell of the rare earth ion (Yb (³⁺)). It is also different from

The ΕΡ 1,790,701 Β1 source of the reduced heteropolyacids (phosphomolybdic acid) disclosed in US 4,244,741, which is due to transitions of common electronic charge transfer in the complex molecular ion rather than the transition in the isolated d shell of the molybdenum atom.

[0034] The source of IR absorption in the gravure printing inks disclosed herein is further markedly different from the narrow band near infrared absorbing organic cyanine dyes of EP-A-0 608 118, as well as the broadband nigrosine dyes of US 3 705 043, and from other organic dyes such as IR absorbing phthalocyanines and related compounds. The light absorption properties of said organic dyes are clearly related to their extended molecular π-electron system, including the β-electron shells of carbon and other atoms. Such extended π systems, however, have the disadvantage of increased chemical reactivity; with some exceptions, most of the known organic dye molecules therefore have a poor stability under the influence of the environment (light, moisture, atmospheric oxygen).

[0035] The IR absorbers of the present invention are not based on common interatomic or interionic effects of absorption of atoms or ions within molecules or solid compounds, such as charge transfer bands between valences of "mixed valence" compounds (Prussian blue, etc.) or band absorption forbidden semiconductor materials (GaAs, etc.); on the contrary, the compounds considered here are based only on the intra-atomic (respectively intra-ionic) properties of the dd electronic transitions. Such dd transitions are primarily a property of the isolated atoms or ions, although they are to some extent also influenced by the chemical environment of the atom or ion.

[0036] Preferred IR-absorbing substances in the context of the present invention are copper (II) and / or iron (II) compounds, e.g. phosphates of these elements, preferably in the form of a solid compound for maximum stability. However, alternatively, the IR-absorbing transition element atoms or ions may also be bonded to a polymeric paint binder component, particularly if the binder component contains specific binding sites for transition element ions, preferably Cu (²⁺) and / or for Fe (²⁺). Such binding sites may be phosphate or phosphonate groups, preferably diester monohydrophosphate groups that are cross-linked or grafted onto the polymer backbone. Alternatively, the IR-absorbing complex of a transition element atom or ion and a binding site may simply be contained in the polymer, such as, for example, an organic thiourea-copper (II) complex dissolved in a binder.

[0037] In the context of the present invention, a preferred solid IR-absorber containing IR-absorbing transition element atoms or ions is a crystalline compound composed of one or more cations and one or more anions. Preferred anions are selected from rock forming anions, i.e. those which form insoluble oxidized minerals with many different cations such as hydroxide anions, fluoride oxides and anions, as well as various borates, carbonates, aluminates, silicates, phosphates, sulfates, titanates, vanadates, arsenates, molybdates and tungstates. The at least one anion is preferably selected from the group consisting of phosphate (PO₄³), hydrogen phosphate (HPO4²), pyrophosphate (P2O₇^4-), metaphosphate (P3O9³), polyphosphate, silicate (SiO4⁴), condensed polysilicates, titanate (TiO3²), condensed polytanates, vanadate (VO4³), condensed polyanadates, molybdate (MoO4²), condensed polymolybdates, tungstate (WO4^2-), condensed polycarbonates, fluoride (F), oxide (O² ) and hydroxide (OH).

[0038] Preferred IR-absorbing cations, in combination with these anions, are iron (II) (Fe²⁺) and copper (II) (Cu²⁺), alone or in solid solution with their inactive in IR mineralogical compounds of the elements of the same group, e.g. with magnesium (II) (Mg²⁺) for iron (II) and with zinc (II) (Zn²⁺) for copper (II).

[0039] Useful IR-absorbing crystalline compounds in the context of the present invention are those that do not lose a part of their composition, e.g. the water of crystallization contained, when heated to moderately high temperature, i.e. to a temperature not exceeding 400 ° C. Indeed, it has been found advantageous to use dehydrated compounds, suitably previously dehydrated compounds which contain water of crystallization or otherwise lost groups, by heating them in air to a temperature between 200 ° C and 400 ° C for about one to four hours (depending on the compound) until a constant weight is obtained.

[0040] In particular, the following compounds can be used in the invention: copper (II) fluoride (CuF₂), copper hydroxyfluide (CuFOH), copper hydroxide (Cu (OH)₂), copper phosphate (Cu₃(AFTER₄)₂ 2H₂O), anhydrous copper phosphate (Cu₃(AFTER₄)₂), basic copper (II) phosphates (e.g. Cu₂AFTER₄(OH), "libetenite" the formula of which is sometimes written Cu₃(AFTER₄)₂ Cu (OH)₂; Cu₃(AFTER₄) (OH)₃, "Cornet", Cu₅(AFTER₄)₃(OH)₄, "Pseudomalachite", CuAI₆(AFTER₄)₄(OH)₈-5H₂O "turquoise", etc.), copper (II) pyrophosphate (Cu₂(P₂ABOUT₇) 3H₂O), anhydrous copper (II) pyrophosphate (Cu₂(P₂ABOUT₇)), copper (II) metaphosphate (Cu (PO₃)₂, more correctly spelled Cu₃(P₃ABOUT₉)₂), iron (II) fluoride (FeF₂4H₂O), anhydrous iron (II) fluoride (FeF₂), iron (II) phosphate (Fe₃(AFTER₄)₂ 8H₂O, "viwianite"), lithium iron (II) phosphate (LiFePO₄, "Triphilin"), Iron (II) sodium phosphate (NaFePO₄,

ΕΡ 1 790 701 Β1 "marycite"), iron (ll) silicates (Fe₂SiO₄, "Fajalit"; Fe_xMg₂._xSiO₄, "Olivine"), iron (II) carbonate (FeCO₃, "Ankerite", "siderite"); nickel (II) phosphate (Ni₃ (ΡΟ₄)₂8Η₂Ο), or titanium (III) metaphosphate (Ti (P₃ABOUT₉)). Furthermore, the crystalline IR absorber may also be mixed ionic compounds where two or more cations participate in the crystal structure, such as Ca₂Fe (PO₄)₂4H₂Oh, anapaita. Likewise, two or more anions may participate in the structure, as in the aforementioned basic copper phosphates, where OH () is the second anion, or even both together, as in magnesium iron phosphate, MgFe (PO₄) F, "vagnerite".

[0041] The solid IR-absorber may further be glass, containing the IR-absorbing transition element ion or ions. Preferred glasses are phosphate and / or fluoride containing compounds which coordinate the transition element ion or ions with the phosphate and / or fluoride anions present in the glass. It is worth noting that these anions are located at the lower end of the "spectrochemical series", i.e. provide low-energy dd transitions in transition element ions, shifting the ion's absorption bands towards the infrared. "Spectrochemical series" is discussed in ABP Lever, "Inorganic Electronic Spectroscopy", ed. 2, "Studies in Physical and Theoretical Chemistry, vol. 33", Elsevier, Amsterdam, 1984, ch. 9 and the literature cited therein.

[0042] IR-absorbing glasses which may be incorporated in a suitably powdered form in the gravure printing ink disclosed herein are, for example, those of JP 05-279078 A2 and JP 05-093160 A2, documents already cited above.

[0043] Pigments and additives for gravure ink formulations have a statistical particle size preferably not exceeding 50 microns, more preferably not exceeding 20 microns, most preferably not exceeding 10 microns. No single molecule should exceed a size of 100 micrometers (upper cut-off), which is the target usually achieved by the final classification (screening) operation. It is worth noting that too large particles, even in small numbers, cause problems on the printing press as the ink tends to peel off the engraved pattern.

[0044] The specific absorption in the "optical infrared" range (ie, between 700 nm and 2500 nm) of the infrared-absorbing material that is used in the gravure printing ink of the present invention is thus simply due to intra-atomic or intra-ionic dd electron transitions. The absorbing material may, however, in addition to the IR-absorption used, exhibit further dd transition banding in the visible range (i.e. between 400 nm and 700 nm) as well as all types of absorption bands in the ultraviolet region of the spectrum (i.e. below 400 nm).

[0045] The IR-absorbing materials that are used in the gravure printing ink of the present invention, however, are different from the transition metal pigments of the prior art, such as nickel and cobalt pigments used in decorative coatings ("cobalt blue", etc .; US 3,748,165), or iron-based yellow, red and black pigments used in classical printing and coating applications. In these prior art transition metal pigments, the effect of visible absorption is deliberately sought and exploited. The basic idea of ​​the present invention, however, is based on IR absorbing pigments which are not or at most slightly colored in the visible spectral range (400 nm to 700 nm) in order to be compatible with all types of visible ink shades and suitability for invisible marking.

[0046] Preferred IR-absorbing substances in the paint according to the present invention are therefore those which are substantially non-absorbing in the visible range of the spectrum (400 nm to 700 nm), i.e. those whose CIE (1976) value of the brightness of the scattered reflected light (L *) is greater than 70, preferably greater than 80 as measured by the powder without solvent.

[0047] To obtain a sufficiently strong absorption effect, the IR-absorbing transition metal atoms or ions must be present at rather high concentration in the IR-absorbing material; typically at a concentration by weight of 10% or greater, preferably 20% or greater, and even more preferably 40% or greater. The IR-absorbing materials used in the gravure printing ink of the present invention are therefore different from transition element-containing luminescent compounds such as ruby ​​(Al₂ABOUT₃: Cr) or transition metal doped grenades (cf. US 3,550,033) and other crystals used in laser applications. It is noteworthy that these luminescent compounds contain sensitizing or emitting transition metal ions simply at the low concentrations that are appropriate for obtaining such luminescent effects.

[0048] Furthermore, the gravure ink of the present invention must contain the IR-absorbing material in a sufficiently high concentration to obtain good contrast on the printed document in a given IR range of the spectrum. Useful concentrations of the absorbent substance in the paint range from 5% to 70%, preferably 10% to 50%, even more preferably 20% to 50% by weight of the paint; these concentration levels are significantly higher than the concentration levels used for luminescent markers.

EP 1 790 701 Β1

[0049] The concentration level of the IR-absorbing substance may further vary depending on the inks used on the same document, to produce darker and brighter infrared zones on the document, respectively, or to print a hidden infrared halftone image. This can be achieved, e.g. in a document, by using at least two IR-absorbing inks according to the invention, wherein the IR-absorbing inks differ in IR absorption levels.

[0050] In another variation, the same ink containing the IR absorbent may be printed with a gravure plate having zones of different engraving depths. This results, in particular for the moderately IR absorbing transition metal compounds used in the present invention, in the infrared and darker zones of the document. Such infrared absorption density modulation can furthermore be masked by the strong visible light-absorbing pigmentation of the gravure ink, so that a difference in the engraving depth is not revealed by the difference in visible color.

[0051] Moreover, the IR-absorbing substance of the present invention, having a broad absorption profile, can be advantageously combined within the same paint with all types of other IR-absorbing substances disclosed in the prior art, and in particular with IR-absorbing organic substances. IR-absorbing organic materials having a narrower absorption peak than transition metal-based IR-absorbing materials are particularly preferred in the present context. Such a combination makes it possible to obtain an even more complex infrared absorption profile and thus increase the technical and security level of the concealed marking. The organic IR-absorbing material may also be present in a second ink, printed on the same document, in order to take advantage of the auto-read contrast generated.

The IR-absorbing gravure ink according to the present invention is preferably used in the production of security materials such as banknotes, passports, checks, coupons, identification cards, transaction cards, seals, excise stamps, etc. The IR-absorbing ink may be overprinted with as a standalone security feature, or may be used in conjunction with non-IR absorbing inks having the same visible shade to provide a hidden IR absorption pattern. Moreover, the IR-absorbing ink according to the present invention can be combined on the same document with other IR-absorbing inks having a composition other than that disclosed in the invention, in particular with inks containing an organic IR absorbent.

[0053] The method of producing an engraved steel die ink according to the present invention comprises the step of incorporating an infrared absorbing substance containing a transition element atom or ion, the infrared absorption of which is due to electron transitions in the d-shell of the transition element atom or ion, into a polymeric organic agent. binding, together with any further substances required.

[0054] The preparation of gravure printing ink, including adjusting its viscosity and its other rheological properties to obtain printing characteristics, and the gravure printing process itself, are known to the skilled person and need not be further explained here.

[0055] The gravure ink according to the present invention will be described below by means of exemplary non-limiting variations.

Fig. 1 shows the IR-absorption characteristics of the copper (II) phosphate glass pigment used in example 1 of the present application.

Fig. 2 shows the IR-absorption characteristics of a copper phosphate white intaglio ink according to example 2 of the present application.

Fig. 3 shows the IR-absorption characteristic of "Triphilin" iron phosphate (LiFePO₄) used in example 3 of this application.

Fig. 4 shows the IR-absorption characteristics of the copper (II) and / or iron (II) phosphate polymers used in example 4 of the present application.

Fig. 5 shows the IR-absorption characteristics of an intaglio printing ink containing copper phosphate and additional organic IR absorbent, according to example 5 of the present application.

EP 1 790 701 Β1

Example 1:

Oxidation-dried gravure ink composition containing phosphate glass as infrared absorber (for paper wipe copperplate engraving process)

[0056]

<td>Product of addition of tung oil and phenolic resin modified with maleic acid in high-boiling mineral oil (PKWF 28/31)</td><td> 25,0</td>

<td>Fatty alkyd resin</td><td> 7,5</td>

<td>Alkylphenol resin modified with crude tung oil</td><td></td>

<td>in Ink Solvent 6/9 (SIC)</td><td> 16,0</td>

<td>Polyethylene wax (melting point 130 ° C)</td><td> 1,5</td>

<td>Calcium carbonate (natural chalk)</td><td> 13,0</td>

<td>IR Absorbing Phosphate Glass Pigment (*)</td><td> 25,0</td>

<td>Color pigment (**)</td><td> 5,0</td>

<td>Ink Solvent 6/9 (SIC) (**)</td><td> 6,0</td>

<td>Desiccant, Cobalt Octanoate (11% metal)</td><td> 0,1</td>

<td>Desiccant, manganese octanoate (10% metal)</td><td> 0,1</td>

<td colspan="2">(*) The glass-ceramic IR-absorbing pigment was prepared by grinding a phosphate glass IR absorbent (Fig. 1) according to US 2004/0082460, Example 1, to an average particle size of 8 to 10 microns. In order to obtain paints with suitable colors but without the IR absorption feature, the IR absorbing pigment was replaced with the same amount of calcium carbonate by weight. (**) The color pigment was selected depending on the desired shade, e.g .: White Cl Pigment White 6 Yellow Cl Pigment Yellow 13 Red Cl Pigment Red 170 Green Cl Pigment Green 7 Blue Cl Pigment Blue 15: 3 Violet Cl Pigment Violet 23 Black Trichrome Black (Cl Pigment Red 170; Cl Pigment Yellow 13; Cl Pigment Blue 15: 3 in the correct ratio). This mixture of pigments is an "IR transparent black" which allows the paint to be transparent in the far optical infrared range. (** *) The viscosity of the ink was adjusted with Ink Solvent 6/9 (Shell Industrial Chemicals) to a value between 5 and 10 Pa s at 40 ° C.</td>

[0057] Color matched pairs of paints with specific visible shades, each shade with and once without IR-absorbent, were produced by mixing all the ingredients of the composition together, except the drying agents, and performing two cycles in a three-roller mill to form 10 homogeneous paint. The drying agents were finally added and mixed for 15 minutes and the finished paint was degassed under vacuum. The viscosity of the paint was adjusted to 10 Pa at 40 ° C.

[0058] The thus obtained inks were printed on banknote paper with a standard gravure press in the form of a pattern containing visible colors and hidden indicia in IR. The IR absorption patterns, useful in automatic money handling, can thus be made fully independent of the visible aspect of the document.

EP 1 790 701 Β1

Example 2:

Oxidation-dried gravure ink composition with sheet feed for copperplate engraving water wipe process

[0059] The water-containing intaglio without spacer inks are prepared according to the following composition:

<td>Macromolecular surfactant as described in US 4,966,628</td><td> 15,0</td>

<td>Alkylphenol adduct of tung oil diluted in high-boiling oil (Magie 500) to a solids content of 80%</td><td> 8,0</td>

<td>Fatty alkyd resin diluted with high-boiling mineral oil (Magie 500) to a solids content of 80%</td><td> 10,0</td>

<td>Sodium salt of sulfonated castor oil in water (solids content 60%)</td><td> 2,0</td>

<td>Micronized polyethylene wax</td><td> 2,0</td>

<td>High-boiling mineral oil (Magie 500)</td><td> 3,0</td>

<td>IR-Absorbing Phosphate Pigment (*)</td><td> 35,0</td>

<td>Cl Pigment White 6</td><td> 3,0</td>

<td>Calcium carbonate</td><td> 15,0</td>

<td>Multi-metal drying agent (cobalt, manganese and zirconium octanoate salts diluted in high-boiling mineral oil to 85% solids content)</td><td> 2,0</td>

<td>Deionized water thickened with cellulose ether (MC or CMC sodium 2.5% to 3.0%) (***)</td><td> 15,0</td>

<td colspan="2">(*) The IR-absorbing phosphate pigment was dehydrated copper phosphate of formula Cu₃(AFTER₄)₂, obtained by heating hydrated copper phosphate for 2 hours at 400 ° C in air. In order to obtain paints with suitable colors but without the IR-absorption feature, the IR-absorbing pigment was replaced with the same amount of calcium carbonate by weight. (***) The cellulose ether was selected from the group consisting of methyl cellulose (MC) and / or sodium carboxymethyl cellulose (sodium CMC) and used as described by C. Baker, The Book and Paper Group Annual, Vol. 1, 1982.</td>

[0060] Color matched pairs of white paints, with and without IR-absorbent, were prepared by mixing all the components of the composition together, except the drying agents and water, for a total of 20 minutes at room temperature in a Molteni mixer, followed by two cycles. in a three-roller mill to create a uniform paint. The drying agent and water were finally added and mixed for 15 minutes and the finished paint was degassed under vacuum in a Molteni mixer. The viscosity of the paint was adjusted to 10 Pa at 40 ° C.

Example 3

[0061] The UV curable cationic polymerizing gravure ink was prepared in a conventional manner (i.e. by premixing all ingredients, then performing two cycles in a three roller mill) according to the following composition:

<td>A cationic polymerizing varnish as described in US 5,658,964</td><td> 44,0</td>

<td>Onium salt initiator (CYRACURE UVI 6974-Union Carbide)</td><td> 7,0</td>

<td>IR-Absorbing Phosphate Pigment (*)</td><td> 15,0</td>

<td>Color pigment (**)</td><td> 3,0</td>

<td>Silicon Dioxide (AEROSIL 200 --Degussa)</td><td> 15,0</td>

<td>Micronized polyethylene wax (CERIDUST 9615A-Hoechst)</td><td> 5,0</td>

EP 1 790 701 Β1

<td>Surfactant (SILWET L 7604 — Union Carbide)</td><td> 1,0</td>

<td>Viscosity Regulator (TRIETHYLENE GLYCOL-Dow Chemicals)</td><td> 10,0</td>

<td colspan="2">(*) The IR-absorbing phosphate pigment was lithium iron (II) phosphate (LiFePO₄, "Triphilin"), having an absorption spectrum given in Fig. 3. In order to obtain paints with suitable colors but without the IR-absorption feature, the IR-absorbing pigment was replaced with the same amount of calcium carbonate by weight. (**) The color pigment was selected according to the desired shade as given in Example 1.</td>

[0062] The viscosity of the paint was adjusted to 12.5 Pa s at 40 ° C. It showed an excellent reaction to the curing with UV light as well as a very good dark shade after curing. The inks were non-washable and met all requirements for an engraved steel die inks for use in printing security materials.

Example 4

UV-cured urethane acrylate gravure printing ink containing IR absorbing phosphate resin:

[0063]

<td>Urethane acrylate reactive monomer</td><td> 26,6</td>

<td>IR-absorbing monomer (*)</td><td> 20,0</td>

<td>Carnauba wax</td><td> 4,0</td>

<td>Sodium dodecylbenzene sulfonate</td><td> 3,0</td>

<td>UV stabilizer (Florstab UV-1)</td><td> 2,0</td>

<td>Color pigment (**)</td><td> 5,0</td>

<td>Filler (CaCO₃) (***)</td><td> 33,0</td>

<td>ESACURE® ΙΤΧ</td><td> 2,6</td>

<td>IRGACURE 369</td><td> 3,8</td>

<td colspan="2">(*) IR-absorbing monomer was prepared according to US 5,466,755, example 1 (cf. Fig. 4, curve 1) or example 2 (cf. Fig. 4, curve 2); the indicated monomers and the copper (II) salt, respectively the copper (II) and iron (II) salts were mixed together under heat (60 ° C) without however adding the polymerization initiator. (**) The color pigment was selected according to the desired shade as given in Example 1. (***) The viscosity of the paint has been adjusted to above 5 Pa s at 40 ° C. It showed a good response to curing with long wavelength UV light.</td>

[0064] Printed documents such as banknote, passport, check, voucher, identification or transaction card, stamp, excise stamp, etc., containing the ink according to the invention, as shown in particular in the examples, were prepared by printing the ink on a standard gravure press. The IR-absorbing ink was printed as a standalone security feature or, alternatively, used in conjunction with IR non-absorbing inks having the same visible shade to provide hidden IR absorption patterns, in addition to the visible features, on these documents.

ΕΡ 1 790 701 Β1

Example 5

Gravure oxidative ink with additional specific IR absorption peaks (related to Fig. 5)

[0065]

<td>Product of addition of tung oil and phenolic resin modified with maleic acid in high-boiling mineral oil (PKWF 28/31)</td><td> 25,05</td>

<td>Fatty alkyd resin</td><td> 7,5</td>

<td>Alkylphenol resin modified with crude tung oil in paint solvent 6/9 (Shell Industrial Chemicals)</td><td> 16,0</td>

<td>Polyethylene wax</td><td> 1,5</td>

<td>Calcium carbonate</td><td> 19,0</td>

<td>Dehydrated copper phosphate with the formula Cu₃(AFTER₄) 2, obtained by heating hydrated copper phosphate for 2 hours at 400 ° C in air</td><td> 25,0</td>

<td>Hexadeka- (3-ethoxy-1-thiophenolate) -phthalocyanate-zinc (II)</td><td> 0,15</td>

<td>Paint Solvent 6/9 (Shell Industrial Chemicals)</td><td> 5,0</td>

<td>Cobalt Octanoate (11% metal)</td><td> 0,1</td>

<td>Manganese octanoate (10% metal)</td><td> 0,1</td>

[0066] The paint was prepared as described above.

ΕΡ 1 790 701 Β1