MX2008006692A - Ir-absorbing intaglio ink - Google Patents

Abstract

Pasty ink for the engraved steel die printing process, having a viscosity value above 3 Pa.s, preferably above 5 Pa.s at 40°C, and comprising an infrared absorbing material, wherein said infrared absorbing material is a transition element compound whose IR-absorption is a consequence of electronic transitions within the d-shell of transition element atoms or ions.

Description

INK FOR HUECOGRABADO THAT ABSORBES IN THE INFRARED FIELD OF THE INVENTION The present invention pertains to the field of inks and coating compositions. In particular, it refers to an ink for the printing process with engraved steel plate (copper plate, gravure), which is used to print currency and other security documents. More particularly, 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 thereof.

BACKGROUND OF THE INVENTION Those with experience know the compounds and coatings that absorb radiation in the 'optical infrared' range of the electromagnetic spectrum, ie wavelengths between 700 nm and 2,500 nm. Said materials are used as absorbers of solar energy, as well as to produce hidden, legible marks with a machine on objects or documents, for the automated process or authentication of said objects or documents by machines.

Throughout the present description, the expressions 'infrared' or 'IR' are used to designate the spectral range of wavelengths between 700nm and 2 500nm. The term 'visible' will designate the spectral range of wavelengths between 400nm and 700nm. . The term 'ultraviolet' or 'UV' will be applied at wavelengths shorter than 400nm. In addition, the expressions 'near infrared' or 'NIR' are used to designate the spectral range of wavelengths between 700nm and 1 lOOnm, which corresponds to the radiation detected by the usual silicon photodetectors Throughout the present description, the terms "printing process with engraved steel plate", "printing process with copper plate", and "gravure printing process" are They use as synonyms for the same printing technique. A first group of the first patents on infrared-related printing technologies related exclusively to aspects of the process. US 3 705 043 (Zabiak) discloses an ink composition that absorbs in the infrared (which absorbs in the IR) for printing by ink jet, for the printing of machine-readable bar codes At the time of said presentation (1972) ), for technical reasons, barcode readers were limited to the range 'near infrared' (700nm - llOOnm) of the spectrum; for this reason an organic tincture of nigrosine absorbing it in the infrared was added to the ink, to make it also 'visible to the machine' A technique for a similar purpose was presented in US 3,870,528 (Edds et al., IBM) , and in US 4,244,741 (Kruse, US Postal Service); this latter patent describes the use of a heteropoly- (osphomolybd-) reduced acid as an inorganic infrared absorbent. It can be summarized that these publications did not refer to the use of substances that absorb in the IR as safety marks. A second group of publications related to security documents: EP-A-0 552 047 (Nishida et al, Hitacha Maxell Ltd) discloses a security document with a printed infrared absorbing trademark, comprising a colored concealment layer for hide the security element that absorbs in the IR in the visible spectral range of 400nm - 700nm The IR absorbers according to the description of EP-A-0 552 047 must be used in conjunction with layers of concealment that make their existence and position to the naked oo. EP-A-0 263 446 (Abe et al., Damichise ka Color &Chemicals Mfg. Co. Ltd.) discloses an anti-copy print comprising covert information in a security document, as well as a method for producing said print , where I know uses a black ink that absorbs in the IR in addition to the process of inking to four standard colors, transparent to the IR, and in conjunction with it. The 'black that absorbs in the IR' is preferably black smoke, which absorbs indiscriminately throughout the entire visible and infrared spectral range, while the 'IR transparent black' is an organic dye that absorbs only in the visible range of the spectrum. In the field of automated paper money processing, IR absorption plays an important role. Most of the currency currently in circulation not only carries visible colored prints, but also specific features that are detected only in the infrared part of the spectrum. In general, these IR characteristics are implemented to be used by equipment for automatic currency processing, in banking and automated sales applications (ATMs, automated vending machines, etc.), to recognize a specific currency bill and to verifying its authenticity, in particular to discriminate against forgeries made by color copiers WO-A-04/016442 (Banque de France) deals with documents protected by a material that absorbs in the infrared.

The visible (black) appearance of inks that absorb in the infrared according to EP-A-0 263 446 is perceived as a disadvantage in security applications, where IR absorption should be used as an additional, covert feature. say invisible One way to obviate this difficulty may be to mimic the ink absorbed in the IR by overprinting, or by using pairs of inks that absorb in the IR and transparent to the IR with the same visible color; however, the last option imposes a quite restrictive limitation on the document designer, since it is not compatible with clear shading. Another group of patents reveals invisible IR absorbers, which can be used in inks of all shades (even white), without contributing to their visible appearance: EP-A-0 608 118 (Yoshmaga et al., Canon KK) reveals a medium (such as a paper currency, security document, etc.), with invisible information recorded, as a means of legible recognition with a machine for security documents, to prevent copying in copying machines. The record is made using organic materials of the type of the cyanmas that absorb in the near infrared, which are colorless and transparent in the visible part of the spectrum, and therefore are invisible to the human eye. A similar approach was developed by Tashima et al., Damippon Ppnting Co. Ltd., who disclose the use of inorganic ytterbium phosphate (YbP04) as an invisible security element, which absorbs into the IR, as well as the corresponding inks and coating compositions that contain it, along with security documents and security patterns that can be done 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 Pat. No. 5,911,921 (Takai et al., Shin-Etsu Chemical Co., Ltd.) discloses a non-stoichiometric phosphate of ytterbium of even lower reflectivity in the infrared, to be used as a safety material that absorbs in the IR. The organic and inorganic IR absorbers of this last group of documents thus solve the disadvantages of the visible coloration of the IR absorber; however, there is another noteworthy disadvantage related to its use, which is the rather narrow spectral width of the absorption bands in the infrared that show the organic dyes of the type of cyan and the IR absorber of YbP04. It is noteworthy that the detection (reading) of narrow band IR absorption characteristics requires a detector equipment adapted in particular to read the precise absorption wavelength in question, and, in the case of YbP04, the use of a relatively high concentration of the material absorbed in the IR in the printing ink. There are currently a large number of different models of equipment to process currency from many suppliers around the world. These equipments, although they allow to control the IR absorption of the paper money, do not work in any way in a single IR wavelength and always there, currently there is no 'standard IR color', analogous to the CIELAB standard that is used in the Visible colonmetry. Therefore, narrowband IR absorbers are not compatible with generic coin process applications, due to compatibility reasons with existing process equipment. It should be mentioned that it is not usually feasible to adapt the existing equipment to process currency in automatic banking and automated sale applications with a new type of security element that absorbs in the IR. On the other hand, the classic option of using carbon black as an indiscriminate, broadband IR absorber has the aforementioned disadvantage of restricting the paper currency designer to only dark or black shades. To this is added the general availability of said type of materials; therefore, the carbon black, although it is an IR absorber, may not be considered a material ofsafety The same is true for semi-metallic graphite material, whose use as a pigment absorbing in the IR in security documents was revealed by Murl in WO-A-98/28374 Ideally, the IR absorber for coin process applications it should be transparent in the visible range (400nm to 700nm), for example to allow its use in all types of visibly colored inks and also in marks that are invisible to the naked eye, and should show strong absorption in the near infrared range ( 700nm to 1 lOOnm), for example to allow easy recognition by standard equipment to process currency (based on IR silicon photodetectors, which are sensitive up to 1 lOOnm). The IR absorber should also be transparent, again somewhere in the range between l.lOOnm and 2.500nm, to allow discrimination of the specific security feature of the coin, from a simple impression with black smoke or graphite, which absorbs indiscriminately over the entire IR range Such discrimination can be carried out for example by means of a simple transparency control in the region of 1 100-2 500nm, using an appropriate photoelectric cell (Ge, InGaAs, etc.). Printing with steel plate (copper plate, gravure) is a very specific method for the production of currency and other high security state documents. Gravure printing machines are heavy and expensive equipment, which is not available for other commercial printing applications, and is used exclusively in the few high security printing facilities in the world. As a consequence, even a security feature of modest physical sophistication can be taken at the high security level if it is applied through a gravure printing process. For prior art references related to inks for the steel plate printing process see 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 inventors; where the contents of said documents are included here for reference. Gravure inks for security printing are characterized by their pasty consistency (with a rather high viscosity value, greater than 3, preferably greater than 5 Pascal * sec (Pa.s) at 40 ° C) and, in particular, by its high solids content, typically greater than 50% by weight. In addition, security documents such as paper money should be durable and resistant to sunlight and environmental influences (ie humidity, oxygen, laundry and commonly available solvents and chemicals). Therefore, to print such documents ink formulations with particularly good strength are used, which comprise epoxy-ester or high-yield urethane binder resins. Due to the same reason, inorganic compounds are preferably selected for pigments, fillers, and other solids comprised in a gravure ink; however, organic pigments with a proved high resistance can also be used.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ink for gravure printing that meets the above requirements. It has now been surprisingly discovered that the above object is solved by an ink for the printing process with etched steel plate, where said ink comprises a polymeric organic binder, a material that absorbs in the infrared, and, if necessary, solvent and / or filler, wherein said ink has a pasty consistency with a viscosity value of at least 3, preferably 5 Pa.s at 40 ° C, and where said infrared absorbing material comprises atoms or ions of transition elements whose absorption in the infrared it is a consequence of electronic transitions within the layer d of the atoms or ions of transition elements.

Surprisingly, we have discovered a class of materials that are suitable as broadband IR absorbers in gravure printing inks, which meet those requirements and solve the disadvantages of both narrow band IR absorbers and indiscriminate IR absorbents. of black smoke or graphite These materials that absorb in the infrared, which may be organic or inorganic nature, are characterized because they contain specific chemical elements with an incomplete electronic layer (ie atoms or ions of transition elements), and whose infrared absorption is a consequence of the electronic transitions within said layer d of the atom oi on It was discovered that certain compounds of atoms or appropriate ions of transition elements absorb in the range NIR (700nm to l.lOOnm), while they are almost transparent in the visible range (400nm to 700nm) of the spectrum, as well as in a certain range between l.lOOnm and 2 500nm. Despite the fact that said materials only show a moderately strong absorption in said NIR range, they can be applied by gravure printing, in such a way that a sufficient quantity of absorbing material is transferred in the IR on the document of security to result in a useful IR contrast (absorption density).

DESCRIPTION OF THE INVENTION Persons with experience in inorganic spectroscopy know the electronic d-d transitions, which occur within the incomplete layer of an atom or ion of a transition element. In this context, reference is made to A.B.P. Lever, "Inorganic Electronic Spectroscopy", 2nd edition, "Studies m Physical and Theoretical Chemistry, Vol. 33", Elsevier, Amsterdam, 1984, Chapter 6. The terms 'transition element' or 'transition metal' will apply in the context of the present invention to the sequences of chemical elements No. 22 (Ti) to 29 (Cu), No. 40 (Zr) to 47 (Ag), and No. 72 (Hf) to 79 (Au) of the Table Periodic, with particular emphasis on the first transition 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 a titanium (III) ion, vanadium (IV) = vanadyl, chromium (V), iron (II), nickel (II), cobalt (II) or copper (II) (corresponding to the chemical formulas T? 3t-, V02t-, Cr5 +, Fe2 +, N? 2+, Co2 +, and Cu2 +).

In addition, in said compound there may be present more than one atom or ion of transition elements, as well as others atoms or ions (cations or anions), either by structural reasons, or to take advantage of a cumulative effect. The materials whose absorption of light is a consequence of electronic transitions within the layer d of atoms or ions of transition elements show a barely moderate specific absorption. Therefore, its lack of specific absorption of light must be compensated for by a correspondingly large amount of material, that is, a layer of material thick enough to produce the required absorption property must be present. For this reason, the materials with IR absorption based on transitions in the d layer of the prior art were applied either in a thick coating layer (paints that absorb in the IR for solar panels), or were used as a load in the mass of a plastic material However, the infrared absorbers based on transition elements of the d layer have not been used in common printing applications, where the thickness of the available layer varies within the range between just a few micrometers in offset and flexographic printing, at most between 10 and 15 micrometers of dry residue in screen printing applications, and where only a fraction of the total thickness of the layer represents the pigment load. With this restriction, someone with experience in the art of the formulation of inks prefers to use a material that absorbs in the IR that shows a high specific absorption in the infrared, to achieve the desired result with a small amount of material. It has been found that by using the gravure printing process, it is possible to transfer a fairly thick layer (up to 50 microns) of a high solids ink onto a substrate. Therefore, when using the gravure printing process, it is possible to apply a sufficient amount of said materials with IR absorption based on transitions in the layer d, on a document, in such a way as to obtain a useful infrared contrast. In addition, the materials that absorb in the IR that are commonly revealed can not be obtained for printing applications, which makes them suitable for use in security printing, due to the absence of easy opportunities for counterfeiting. The properties of the compounds of transition elements that absorb in the infrared are known and are already used in certain areas of technology. The iron (II) and copper (II) compounds, with an Fe (2+) or Cu (2+) ion in an appropriate chemical environment, have proven to be efficient broadband IR absorbing materials in the near infrared range. The appropriate compounds of iron (II) or copper (II) are transparent in the visible range of the spectrum - showing at most a slightly yellowish or bluish hue - and are stable under ambient conditions (ie before exposure to oxygen and moisture) . An 'appropriate chemical environment' is for example a phosphate or polyphosphate ion, or, more generally, a group containing phosphorus and oxygen; In many of the IR-absorbing materials disclosed in the prior art, there is a Cu (2+) or Fe (2+) ion linked in fact by an oxygen atom to a phosphorus atom, forming a sequence of MOP atoms. US 4,296,214 (Kamada et al., Mitsubishi Rayon Co, Ltd.) disclose an acrylic ream for solar absorption with copolymerized copolymerized acrylic diphosphonate esters containing copper (II) therein. US Pat. No. 5,466,755 (Sakagami et al., Kureha Kagaku Kogyo KK) discloses an optical filter plastic material, based on monoacid diester-phosphate and monoester-phosphate diacid groups containing acrylic copolymer, in which copper (II) ions are incorporated. and / or iron (II). US 6,410,613 (Ohnishi et al., Kureha Kagaku Kogyo K.K.) deals with other phosphate ester polymers that absorb in the IR comprising copper ions. Said pollen materials are useful as absorbers in the near infrared (filters) in the range of lengths of wave between 700nm and 1200nm, but until now have not been used in inks for printing. US 5,236,633 and US 5,354,514 (Satake et al., Jujo Paper Co., Ltd.) describe near infrared absorbing materials based on a transparent thermoplastic polymer (polymethacrylate, polycarbonate, polyethylene, vmyl chloride, etc.), an organic compound of thiourea, and a copper compound, which melt together to give a plastic material transparent to visible light (slightly bluish), which absorbs into the IR. US 5,723,075 (Hayasaka, Nippon Paper Industries, Co., Ltd.) discloses a similar technology, except that dimerized organic thiourea derivatives are used. US Patents 2,265,437 and US 5,800,861, issued to The Sherwin-Williams Company, disclose the use of, among other things, copper phosphate, basic copper phosphate, and copper pyrophosphate in coatings that absorb in the IR for produce passive solar collectors and so on. Said coatings are characterized in that they have, in addition to their absorption in the visible range, a wide absorption band in the region between 700nm and 1 POOnm. Glasses containing phosphate and / or fluoride comprising copper (2+) ions as IR absorbers have also been used, in particular for IR-cut filters in the optical industry. US 5,173,212 (Speit et al., Schott Glaswerke) and US 2004/0082460 (Yamano et al., HOYA Corporation) disclose corresponding glass formulas and the absorption spectra of the resulting light. JP 05-279078 A2 (Manabe et al., Asahi Glass Co.

Ltd.) reveals a material that absorbs in the near infrared to apply by sepíp printing, which is a powder of colorless glass with copper (II) and phosphoric acid, mixed with a material of ream, which is used for machine reading of information by laser light in the near infrared. JP 06-207161 A2 (Usui et al., Asahi Glass Co., Ltd.) discloses another ink for scrigmatic printing containing copper (II) phosphates, as an absorber for semiconductor laser light (810nm). JP 05-093160 A2 (Matsudaira, Toppan Prmtmg Co., Ltd.) discloses an ink for two-component screen printing for the printing of classified, invisible information. The ink comprises, as the IR absorber, a phosphate glass powder containing iron (II) and / or copper (II) oxide (from Asahi Glass Co. Ltd.). JP 06-107985 A2 (Matsudaira et al., Toppan Printing Co., Ltd.) reveals another two-component ink absorbing in IR, based on copper (II) and / or copper / iron (II) phosphates, vitreous, white , as an absorbent IR. These inks are used for the printing of legible barcodes with a machine in documents of security, such as for example long-term plastic credit cards, identity cards, etc., where the printed information must be read by a semiconductor laser that emits in the near infrared. However, printing inks with etched steel plate (copper plate, gravure), comprising such classes of broadband absorption compounds in the near infrared containing copper (II) or other atom, have not been revealed until now. ion of transition elements. The ink for the engraved steel plate printing process of the present invention comprises an organic binder resin, preferably of the high strength epoxy ester, urethane-alkyd or UV curing type, as well as an absorbing material in the infrared according to the invention, optionally one or more pigments to produce the desired visible color, optionally fillers and / or solvent to adjust the viscosity of the ink to a value greater than 3 Pa.s, preferably greater than 5 Pa.sup.40 ° C, and optionally additional additives, such as, for example, drying agents (drying agents), photomatics, waxes, and rheological additives. This material that absorbs in the infrared is a compound of transition elements whose IR absorption is due to electronic transitions within the layer d of atoms or Transition element ions Those with experience know the formulation of gravure inks and the materials that are commonly used to make gravure inks (ie binders, fillers, solvents, pigments and other additives for inks) and it is not necessary to delve here its disclosure. The origin of IR absorption in the gravure printing inks disclosed herein is different from that of the YbP04 IR absorber disclosed by Tashima et al (for example JP 08-143853), which is a narrow band absorption and due to an electronic transition within the f layer of an ion of a rare earth (Yb (3+)). This is also different from that of the reduced heteropoly acids (phosphomolybdic acid) that reveals US 4 244 741, which is due to transitions by cooperative electronic charge transfer within a complex molecular ion, rather than to a transition within the electron layer. of an isolated molybdenum atom The origin of the IR absorption of the gravure printing inks that are revealed here is also clearly different from the origin of the IR absorption of the organic dyes of the type of cyanmes with narrow band absorption in the infrared EP-A-0 608 118, as well as the origin of IR absorption of Mgrosma dyes with broad band absorption of US 3,705,043, and other organic dyes, such as phthalocyanins that absorb in the IR and related compounds. The light absorption properties of the organic dyes mentioned are remarkably related to its extensive molecular system of p electrons, which relates the electronic layers to p of carbon and the other atoms. Said extensive systems p, however, have the disadvantage of a greater chemical reactivity; for this reason, except for a few exceptions, most known organic dye molecules are not very stable under environmental influence (light, moisture, atmospheric oxygen). The IR absorbers of the present invention are not based on teratomic or etheric ionic or ionic cooperative absorption effects within molecules or compounds in the solid state, for example as the load transfer bands mvalence of 'mixed valence' compounds. (Prussian blue, etc.) or in band gap absorption of semiconductor materials (GaAs, etc.); On the contrary, the compounds considered here are based on the property of the intraatomic (respectively mtrasionic) d-d transitions. Said transitions d-d are in principle a property of isolated atoms or ions, although to a certain degree they are also influenced by the chemical environment of the atom or ion. The preferred IR-absorbing materials in the context of the present invention are copper (II) and / or iron (II) compounds, for example the phosphates of said elements, and preferably in the form of a solid state compound for maximum durability However, alternatively, the atoms or ions of transition elements that absorb in the IR may also be attached to a component of the polymeric binder of the ink, in particular if the binder component contains specific binding sites for transition element ions. , preferably for Cu (2+), and / or for Fe (2+). Said binding sites can be phosphate or phosphonate groups, preferably monoacid phosphate diester groups, which are crosslinked in a polymeric backbone, or grafted thereon. Alternatively, the complex that absorbs in the IR between an atom or ion of a transition element and a binding site can simply be contained in the polymer, for example as an organic thioruea-copper (II) complex, dissolved in the binder . In the context of the present invention, a preferred solid state IR absorber, comprising the atoms or ions of transition elements that absorb in IR, is a crystalline compound, composed of one or more cations and one or more anions. Preferred anions are selected from anions that form rocks, ie those that form more oxygenated minerals with a wide variety of cations, such as hydroxide, oxide, and fluoride anions, as well as various borates, carbonates, alummates, silicates , phosphates, sulphates, titanates, vanadates, arsenates, molybdates and tungstates. Preferably, at least one anion is selected from the group consisting of phosphate (P03 ~), acid phosphate (HPO ,, 2), pyrophosphate (P207 ~), metaphosphate (P-sOc, 3), polyphosphate, silicate (S? 044 ~), condensed polysilicates, titanate (T? 03"~), condensed polyteatinates, vanadate (V043 ~), condensed polyvanadates, molybdate (Mo042), condensed polnadates , tungstate (W042), condensed polyungstates, fluoride (F "), oxide (O2"), and hydroxide (OH "). The preferred IR-absorbing cations, in combination with said anions, are iron (II) (Fe +) and copper (II) (Cu2 +), either alone, or in solid solution with their mineralogical congeners inactive before the IR, example with magnesium (II) (Mg2 +) in the case of iron (II), and with zinc (II) (Zn2 +) in the case of copper (II). The IR-absorbing crystalline compounds that are useful in the context of the present invention are those that do not lose part of their composition, for example the water of crystallization included, when they are heated to a moderately high temperature, that is to say up to a temperature that does not exceed 400 ° C. In fact, it has been discovered that it is advantageous to use dehydrated compounds, respectively by first dehydrating those compounds which contain water of crystallization or other groups that can be released, by heating them to the air up to a temperature between 200 ° C and 400 ° C for between about one and four hours (depending on the compound in question), until reaching a constant weight. Specifically, the following compounds can be used in the invention: copper (II) fluoride (CuF2), copper hydroxyfluoride (CuFOH), copper hydroxide (Cu (OH) 2), copper phosphate (Cu3 (P04) 2 * 2H20), anhydrous copper phosphate (Cu3 (PO,) 2), basic copper (II) phosphates (for example Cu2P04 (OH), "Libetenite" whose formula is sometimes written Cu3 (P04) 2 * Cu (OH ) 2; Cu3 (P04) (OH) 3, "Cornetite", Cu5 (P04) 3 (OH), "Pseudomalachite", CuAl6 (PO 4 (OH) 8 5H20"Turquoise", etc., copper pyrophosphate (II ) (Cu2 (P207) * 3H20), copper (II) pyrophosphate anhydrous (Cu2 (P207)), copper metaphosphate (II) (Cu (P03) 2, which is more correctly spelled Cu3 (P3? 9) 2) , iron (II) fluoride (FeF2 * 4H20), anhydrous iron (II) fluoride (FeF2), iron (II) phosphate (Fe3 (P04) 2 * 8H20, "Vivianite"), lithium iron (II) phosphate (L? FeP04, "Tnfílina"), sodium and iron (II) phosphate (NaFeP04, "Maricita"), iron (II) silicates (Fe2S? 04, "Fayalita"; , Mg2-S? 04, "Olivmo"), iron carbonate (II) (FeC03, "Ankerite", "Siderite"); nickel (II) phosphate (N? 3 (P04) 2 * 8H20), or titanium (III) metaphosphate (T? (P309)). In addition, the crystalline IR absorber can also contain mixed cos ionic compounds, where two or more cations participate in the crystalline structure, for example, as in Ca2Fe (P04) 2 * 4H20, "Anapaite". Similarly, two or more anions can participate in the structure as in the above mentioned basic copper phosphates, where OH C) is the second anion, or even both together, as in magnesium and iron fluorophosphate, MgFe (P04) F , "Wagnerita." The IR absorber in the solid state can also be a glass, comprising the ion or ions of transition elements that absorb in the IR. The preferred glasses are of the types comprising phosphate and / or fluoride, in which there is coordination of the ion or ions of transition elements with the phosphate and / or fluoride anions present in the glass. Said anions are located notably at the lower end of the "spectrochemical series", that is to say they provide transitions d-d of ba to energy of the transition element ions, which push the absorption bands of the ion towards the infrared. With respect to the "spectrum-chemical", the reader is referred to A.B.P. Lever, "Inorganic Electronic Spectroscopy", 2nd edition, "Studies m Physical and Theoretical Chemistry, Vol. 33", Elsevier, Amsterdam, 1984, Chapter 9 and references cited therein. The glass that absorbs in the IR that can be introduced to the gravure printing ink that is disclosed here in the corresponding powder form are, for example, those of JP 05-279078 A2 and JP 05-093160 A2, the documents of which were already cited previously. The pigments and additives for gravure ink formulations have a statistical particle size that preferably does not exceed 50 microns, more preferably does not exceed 20 microns, even more preferably does not exceed 10 microns. Absolutely no individual particle will exceed a size of 100 micrometers (upper cutoff limit), a goal that is generally achieved by a final sorting operation (sifting). Too large particles, even in small amounts, cause noticeable problems in the press during printing, since the ink tends to be swept away from the engraved sheet. In this way, the specific absorption in the 'optical infrared' range (ie between 700 nm and 2500 nm) of the material that absorbs in the infrared, which is used in the intaglio ink of the present invention, it is only a consequence of intra-atomic or intra-ionic d-d transitions. However, in addition to taking advantage of this IR absorption, the absorbing material can show other additional dd transition bands in the visible range (ie between 400nm and 700nm), as well as all types of absorption bands in the ultraviolet region of the spectrum (it is say below 400nm). However, the absorbing materials in the IR that are used in the intaglio tmta of the present invention are different from the transition metal pigments of the prior art, such as for example the nickel and cobalt pigments that are used in decorative coatings. ('cobalt blue', etc., US 3 748 165), or the yellow, red, and iron-based black pigments used in classic printing and coating applications. In said transition metal pigments of the prior art, it is sought after and an absorption effect is exploited in the visible range. However, the basic idea of the present invention is based on pigments that absorb in the IR that are not colored in the visible range of the spectrum (400nm to 700nm), or that at most only are little colored, so that they are compatible with all the nuance classes of visible ink and to be useful as invisible marks. Therefore, the absorbing materials in the IR that are preferred for the ink of the present invention are those that do not absorb substantially in the visible range of the spectrum (400nm to 700nm), ie those whose CIÉ value (1976) of clarity by diffuse reflectance (*) is greater than 70, preferably greater than 80, as measured in pure powder. To obtain a sufficiently strong absorption effect, the atoms or ions of transition metals that absorb in the IR must be present in a fairly high concentration in the material that absorbs in the IR; typically at a concentration of 10% or more, preferably 20% or more, and still more preferably 40% or more, by weight. Therefore, the absorbing materials in the IR that are used in the gravure ink of the present invention are different from the luminescent compounds that contain transition elements, such as ruby (Al203: Cr) or garnet doped with metal of transition (see US 3,550,033) and other crystals that are used in laser applications. It is noteworthy that said luminescent compounds contain the transition metal ions sensitizing or emitting only at low concentrations, which are appropriate to produce said luminescence effects. Furthermore, the gravure ink of the present invention must contain the material absorbing in the IR at a sufficiently high concentration level, in such a manner as to produce good contrast in the printed document in said IR range of the spectrum. Useful concentrations of the absorbent material in the ink vary within the range between 5% and 70%, preferably between 10% and 50%, even more preferably between 20% and 50%, by weight of the ink, said concentration levels are significantly greater than the concentration levels used in the case of phosphorescent markers. Furthermore, said level of concentration of the material absorbed in the IR can be varied within the inks used in the same document, to produce more dark and lighter areas in the infrared in the document, or to print a figure hidden grisade that is seen in the infrared, respectively. This can be carried out, for example by means of a document having at least two inks that absorb in the IR according to the invention, where said inks that absorb in the IR differ in their IR absorption level.

In another embodiment, the same ink comprising the IR absorber can be printed with a gravure plate with areas engraved on the sheet with different depths. This results, in particular in the case of the transition metal compounds that absorb moderately in the IR used in the present invention, which remain in the document areas in the infrared are darker or lighter This modulation of absorption density in the infrared can be further mimicked by a strong pigmentation that absorbs in the visible range of the tmta for gravure, in such a way that the depth difference of the engraved sheet is not shown as a difference of the visible color Furthermore, the material absorbing on the IR of the present invention, which provides a wide absorption profile , it can be usefully combined, within the same ink, with all the other types of materials that absorb in the IR that are revealed in art, and in particular with organic materials that absorb in the IR. In this context, organic materials that absorb in the IR with a narrower absorption peak than the materials absorbing in the IR based on transition metals are particularly preferred. This combination makes it possible to produce an absorption profile in the infrared even more complex and thus increase the sophistication and security of the hidden brand. The organic material that absorbs in the IR can also be present in a second ink, printed on the same document, to take advantage of the contrast that is obtained, which is legible with a machine. The gravure ink absorbing in the IR of the present invention is preferably used to produce security documents, such as paper money, passports, checks, vouchers, identity cards, transaction cards, stamps, tax labels, etc. The ink absorbed in the IR can be printed here as either the only safety feature, or it can be used in conjunction with inks that do not absorb in the IR with the same visible hue, to produce a hidden pattern of IR absorption. Furthermore, the ink absorbing in the IR of the present invention can be combined on the same document with other inks that absorb in the IR with a different composition than that disclosed here, in particular with inks containing an organic IR absorber. A process for manufacturing an ink for printing with etched steel plate, according to the present invention, comprises the step of incorporating an infrared absorbing material comprising an atom or ion of a transition element, whose absorption in the infrared is a consequence of electronic transitions within the layer d of said transition element ion or ion, in a polymeric organic binder, together with optional additional materials. Those with experience know how to make a gravure ink, including adjusting its viscosity and its other rheological properties to achieve good printing behavior, and the gravure printing process itself, and it is not necessary to explain them here. Now the gravure ink of the present invention will be further explained with the aid of non-limiting embodiments which serve as an example.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 shows the IR absorption characteristics of the copper (II) phosphate glass pigment used in Example 1 of the present specification. FIG. 2 shows the IR absorption characteristics of a white gravure ink comprising copper phosphate according to Example 2 of the present specification.

Fig. 3 shows the IR absorption characteristics of the iron phosphate "Trifilma" (L? FeP04) which is used in Example 3 of the present specification. Fig. 4 shows the IR absorption characteristics of the copper (II) and / or iron (II) phosphate polymers that are used in Example 4 of the present specification. FIG. 5 shows the IR absorption characteristics of a gravure ink comprising copper phosphate and an additional organic IR absorber, according to Example 5 of the present specification.

EXAMPLES Example 1: Formulation of gravure ink that dries by oxidation, which comprises phosphate glass that absorbs in the infrared (for the paper wipe process of gravure printing with copper plate) Addition product of tung oil and phenolic resin modified with maleic acid in a high-boiling mineral oil (PKWF 28/31) 25, 0 Alkyd ream with high oil content 7.5 Alkylphenolic resin modified with crude tung oil in solvent for 6/9 ink (S.I.C.) 16.0 Polyethylene wax (P.f. 130 ° C) 1,5 Calcium carbonate (natural chalk) 13.0 Pigment absorbing in the phosphate glass IR (*) 25, 0 Colored pigment (**) 5,0 Solvent for Ink 6/9 (S.I.C.) (**) 6.0 Secant of octoate of cobalt (11% of metal) 0.1 Secant of octoate of manganese (10% of metal) 0.1 (*) The glass ceramic pigment that absorbs in the IR was prepared by grinding a glass phosphate IR absorber (Fig. 1) according to US 2004/0082460, Example 1, at an average particle size in the order of 8 to 10 microns. To obtain inks of the corresponding colors, but without the IR absorption characteristic, the pigment absorbing in the IR was replaced by the same amount by weight of calcium carbonate.

(**) The colored pigment was selected according to the desired shade, for example: White Pigment White C.l. 6 Yellow Pigment Yellow C.l. 13 Ro or Pigmento rojo C.l. 170 Green Pigment green C.l. 7 Blue Pigment blue C.l. 15: 3 Violet Pigment Violet C.l. 23 Black Black Trichrome (Pigment red C.l. 170; Pigment Yellow C.l. 13; Pigment blue C.l. 15: 3 in the appropriate proportion). This mixture of pigments is a "transparent black IR" that allows the transparency of the ink in the far infrared optical range. (***) The viscosity of the ink was adjusted with Solvent for Ink 6/9 (Shell Industrial Chemicals) to a value between 5 and 10 Pa.s at 40 ° C. Pairs of inks of the same color of certain visible shades were prepared, each nuance once with the IR absorber and again without it, each time, mixing together all the components of the formula, except for the secants, and carrying out two passes. in a three-roll mill, to obtain a homogeneous ink. The blotters were added at the end and mixed for 15 minutes, and the finished ink was degassed under vacuum. The viscosity of the ink was adjusted to 10 Pa.s at 40 ° C.

The inks that were obtained in that way were used to print with a standard gravure press on paper money in the form of a pattern comprising visible colors and hidden IR features. In this way, IR absorption patterns, useful for the coin-operated process, could be realized with complete independence of the visible aspect of the document.

Example 2: Rotogravure ink drying by sheet-fed oxidation for the rotogravure printing process with copper plate for rinsing with water A non-woven intaglio printing ink was made according to the following formula: Macromolecular surfactant as described in US 4,966,628 15, 0 Alkylphenolic adduct of tung oil diluted in a high boiling point oil (Mag e 500) with a solids content of 80% 8.0 alkyd redox with high long oil diluted in a high boiling point mineral oil (Magie 500) with a solids content of 80% 10.0 Sodium salt of sulphonated castor oil in water (solids content 60%) 2,0 Micronized polyethylene wax 2,0 High Boiling Mineral Oil (Magie 500) 3.0 Pigment to the phosphate that absorbs in the IR (*) 35,0 Pigment White C.l. 6 3.0 Calcium carbonate 15.0 Multi-metal drying (octoate salts of cobalt, manganese and zirconium diluted in a high-boiling mineral oil with a solids content of 85%) 2.0 Deionized water thickened with a cellulose ether (MC or sod-CMC) 2.5% to 3.0%) (***) 15,0 (*) As a pigment to the phosphate absorbing in the IR, dehydrated copper phosphate was used with the formula Cu3 (P04) 2, which was obtained by heating copper hydrous phosphate for 2 hours at 400 ° C in the air. To obtain the inks of the corresponding colors, but without the IR absorption characteristic, the pigment absorbing in the IR was replaced by the same amount by weight of calcium carbonate. (***) The cellulose ether was selected from the group of ethylcellulose (MC) and / or sodium carboxymethylcellulose (sod-CMC) and was used as described in C. Baker, The Book and Paper Group Annual, Vol. 1 , 1982. Pairs of the same color of white inks were prepared, once with the IR absorber and again sm same, mixing together all the components of the formula, except drying and water, for 20 minutes at room temperature in a Molteni mixer, then carrying out two passes through a three-roll mill to achieve a homogenous tmta. The blotter and water were added at the end and mixed for 15 minutes, the resulting tt was degassed under vacuum in a Molteni mixer. The viscosity of the ink was adjusted to 10 Pa.s at 40 ° C.

EXAMPLE 3 A cationically UV-curable polymerisable gravure ink was made in the conventional manner (ie pre-mixing all the ingredients, then carrying out two passes in a three-roll mill) according to the following formula: Cationically polymerizable varnish as described in US 5,658,964 44.0 Initiator based on salt onium (CYRACURE UVI 6974 -Union Carbide) 7.0 Pigment to the phosphate that absorbs in the IR (*) 15,0 Colored pigment (**) 3,0 Smoked silica (AEROSIL 200 --Degussa) 15,0 Micronized polyethylene wax (CERIDUST 9615A-Hoechst) 5,0 Surfactant (SILWET L 7604 - Union Carbide) 1.0 Viscosity regulator (TRIETILENGLICOL- Dow Chemicals) 10.0 (*) As a pigment to the phosphate absorbing in the IR, lithium iron (II) phosphate (L? FeP04, "Tnflima") was selected, with an absorption spectrum as shown in Fig. 3. To obtain the inks of the corresponding colors, but with the IR absorption characteristic, the pigment absorbing in the IR was replaced by the same amount by weight of calcium carbonate. (**) The colored pigment was selected according to the desired shade, as given in Example 1. The tmta was adjusted to a viscosity of 12.5 Pa s at 40 ° C. This showed an excellent curing response with UV light, as well as a very good dark postcuration. The ink could be wiped with paper and met all the requirements that engraved steel plate inks need for use in the printing of security documents.

Example 4 Urethane-acrylate resin UV-curing gravure ink comprising phosphate IR absorbent: urethane-acrylate reactive monomer 26.6 Monomer that absoin the IR (*) 20,0 Carnauba wax 4, 0 Dodecyl sodium benzene sulfonate 3,0 UV stabilizer (Florstab UV-1) 2,0 Colored pigment (**) 5,0 Load (CaC03) (* **) 33.0 ESACURE® ITX 2, 6 IRGACURE 369 3.8 (*) The monomer that absoin the IR was prepared according to US 5.466.755, Example 1 (see Fig. 4, curve 1) or example 2 ( see Fig 4, curve 2); the indicated monomers and the copper (II) salt, respectively the copper (II) and iron (II) salts were mixed together hot (60 ° C), however, without adding a polymerization initiator (** The colored pigment was selected according to the desired shade, as given in Example 1. (***) The ink was adjusted to a viscosity of less than 5 Pa.s at 40 ° C. This showed a good curing response with UV light of long wavelength. Printed documents, such as a paper currency, a passport, a check, a voucher, an identity or transaction card, a stamp, a tax stamp, etc., were made with an ink according to the invention, according to the invention. is given as an example in particular in the given examples, printing with the ink in a standard gravure press. The inks that absorb in the IR were used to print as the only security feature, or, as an alternative, they were combined with inks that do not absorb in the IR of the same hue, to produce hidden IR absorption patterns in addition to the characteristics visible in said documents.

Example 5 Oxidative ink for gravure with additional specific IR absorption peaks (with reference to Fig. 5) Addition product of tung oil and phenolic resin modified with maleic acid in a high-boiling mineral oil (PKWF 28/31) 25, 05 Long alkyd ream of oil 7.5 Resin alkylphenol modified with crude tung oil in Solvent for Ink 6/9 (Shell Industrial Chemicals) 16.0 Polyethylene wax 1.5 Calcium carbonate 19.0 Dehydrated copper phosphate of formula Cu3 (P04) 2, which was obtained heating hydrated copper phosphate during? Hours at 400 ° C in air 25.0 Hexadeca- (3-ethoxy? -l-thiophenolate) - Phthalocyanate of eme (II) 0,15 Solvent for Ink 6/9 (Shell Industrial Chemicals) 5,0 Octoate of cobalt (11% metal) 0,1 Manganese Octoate (10% metal) 0.1 The ink was prepared as described above.

Claims (23)

NOVELTY OF THE INVENTION Having described the invention as above, property is claimed as contained in the following: CLAIMS

1. An ink for the printing process with engraved steel plate, comprising a polymeric organic binder and an infrared absorbing material, where said tmta has a pasty consistency with a viscosity value at 40 ° C of at least 3 Pa .s, preferably at least 5 Pa.s, characterized in that said material that absorbs in the infrared comprises a compound of transition elements and because its absorption in the infrared is a consequence of electronic transitions within the layer d of atoms or ions of transition elements.

The tmta according to claim 1, characterized in that said transition element is selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu.

3. The tmta according to claim 1 or 2, CHARACTERIZED BECAUSE said transition element is an ion that is selected from the group of ions consisting of T 3 3, V 0 2 +, Cr 5 t, Fe 2 +, Ni 2", Co 2 +, and Cu 2 + 4.

The tmta according to any of claims 1 to 3, characterized in that the material which absorbs in the infrared comprising the ion or ions of transition elements that absorb in the IR is a glass, preferably a glass comprising phosphate and / or fluoride, in which there is a coordination of the ion or ions of transition elements with the phosphate and / or fluoride anions present in the glass 5.

The ink according to any of claims 1 to 3, characterized in that the infrared absorbing material comprising the ion or ions of transition elements that absorb in the IR is a crystalline compound, which is composed of one or more cations and one or more anions 6.

The ink according to claim 5, characterized in that an anion is selected from the group consisting of phosphate (P03"), phosphat or acid (HP042"), pyrophosphate (P2074 ~), metaphosphate (P3093"), polyphosphate, silicate (S? 044 ~), condensed polysilicates; titanate (T? 032), condensed polytetranates, vanadate (V043"), condensed polyvanadates, molybdate (Mo042"), condensed polyvanadates, tungstate (W042"), condensed polyungstates, fluoride (F ~), oxide (O2"), and hydroxide (OH ").

The ink according to one of claims 5 or 6, characterized in that the material that absorbs in the infrared is selected from the group of compounds consisting of copper (II) fluoride (CuF2), copper hydroxyfluoride (CuFOH), copper hydroxide (Cu (0H) 2), copper phosphate (Cu3 (P04) 2 * 2H20), anhydrous copper phosphate (Cu3 (P04) 2), basic copper (II) phosphates Cu PO, (OH) ( Libetenite), Cu3 (P04) (OH) 3 (Cornetite), C. { POi), (OH) 4 (Pseudomalakite), CuAl6 (P04) 4 (OH) 8-5H20 (Turquoise), copper (II) pyrophosphate (Cu2 (P207) * 3H20), copper (II) anhydrous pyrophosphate (Cu2) (P207)), copper (II) metaphosphate (Cu3 (P09) 2), iron (II) fluoride (FeF2 * 4H20), anhydrous iron (II) fluoride (FeF2), iron (II) phosphate (Fe , (P04) 2 * 8H20, Vivianite), lithium iron phosphate (II) (L? FeP04, Trifilma), sodium and iron (II) phosphate (NaFeP04, Mancita), iron (II) silicates (Fe_S? 04, Fayalite, Fe Mg2 S? 04, Olivino), iron (II) carbonate (FeC03, Ankepta, Siderite), nickel (II) phosphate (N? 3 (PO,) 2 * 8H20), titanium metaphosphate ( III) (T? (P309)), Ca2Fe (P04) 2 * 4H20, (Anapaite), and MgFe (P04) F, (Wagnerite)

8 The tmta according to any of claims 1 to 3, characterized in that the material that absorbs in the infrared is an atom or element ion of transition that absorbs in the IR attached to a component of the polymeric binder of the ink.

9 The tmta in accordance with the claim 8, characterized in that the polymeric binder of the ink contains specific binding sites for ions of transition elements, preferably for Cu2 +, and / or for Te2 +

10 The ink according to the claim 9, characterized in that said binding sites are phosphate groups that are crosslinked in a main polymeric backbone, or are grafted thereon

11. The tmta according to any of claims 1 to 3, characterized in that the material that absorbs in the infrared is a complex that absorbs in the IR between an atom or ion of a transition element and a binding site contained in the polymer, preferably an organic thioruea-copper (II) complex dissolved in the binder

12 The tmta in accordance with one of the preceding claims, characterized in that the material absorbing in the IR has a value of clarity by diffuse reflectance (L *) CIÉ (1976) greater than 70, preferably greater than 80, as measured in the pure powder.

13. The ink according to one of the preceding claims, characterized in that the material that absorbs in the IR contains atoms or ions of transition elements that absorb in the IR at a concentration of 10% or more, preferably 20% or more, and still more preferably 40% or more, by weight.

The ink according to one of the preceding claims characterized in that it comprises material that absorbs in the IR at a concentration in the range within the range between 5% and 70%, preferably between 10% and 50%, even more preferably between 20 % and 50%, by weight of the ink.

15. The ink in accordance with the claim 14, characterized in that it comprises an additional IR absorber, wherein said additional IR absorbent is an organic compound.

16. The ink in accordance with the claim 15, characterized in that said additional IR absorber shows a narrower IR absorption peak than the material absorbing in the IR based transition metal.

17. A process for making an ink for printing with engraved steel plate according to any of claims 1 to 16, characterized in that it comprises the step of: incorporating an infrared absorbing material comprising a compound of a transition element, whose absorption in the infrared is a consequence of electronic transitions within the layer d of said transition element atoms or ions, in a polymeric organic binder, together with optional additional materials.

Use of an ink for the printing process with engraved steel plate according to any of claims 1 to 16, characterized in that it is for printing a security document, such as a paper money, a passport, a check, a voucher , an identity or transaction card, a stamp, a tax stamp.

19. Security document, such as a paper currency, a passport, a check, a voucher, an identity or transaction card, a stamp, a tax stamp, characterized in that it carries an ink that absorbs in the IR according to the with one of the preceding claims.

20. A security document according to claim 19, characterized in that it has at least two inks that absorb in the IR according to one of the preceding claims, wherein said ink absorbs in the IR differs in its IR absorption levels.

21. Security document according to claim 19, CHARACTERIZED BECAUSE it carries an ink absorbing on the IR that is used for printing using a gravure plate with sheet metal areas engraved with different depth, for example to result in printed areas with different levels IR absorption.

22. Security document according to one of claims 19 to 21, characterized in that it has at least one ink absorbing in the additional IR containing an organic IR absorber.

23. Process for making a security document according to any of claims 19 to 21, characterized in that it comprises the step of applying an ink absorbing on the IR according to one of the claims 1 to 16 on said security document by means of a printing process with engraved steel plate. p.p. Sicpa Holding S.A.