Patent ID: 8187373

Claim:
A printing ink for letterpress and/or offset printing, comprising 5 to 45% by weight of at least one nonpolar solvent with a boiling point of from 200 to 320° C., 20 to 70% by weight of binder, 5 to 25% by weight of colorant absorbing in the visible spectral range and an NIR absorber which has substantially no absorption in the visible spectral range, wherein the solubility of the NIR absorber in the printing ink is at least 0.1% by weight, based on all components of the printing ink, with the proviso that the solubility of the NIR absorber is greater than or equal to the concentration of the NIR absorber in the printing ink, wherein the NIR absorber is an ionic absorber comprising a cyanine cation X + and a corresponding anion 1/mY m− , the cyanine cation having a general formula selected from the group consisting of (I) to (IV) where n is 1 or 2 and the radicals R 1 to R 9 have the following meanings: R 1 and R 2 , independently of one another, are a linear or branched, optionally further substituted alkyl or aralkyl radical having 1 to 20 carbon atoms, R 3 and R 4 , independently of one another, are H or CN, R 5 and R 6 , independently of one another, are one or more, identical or different substituents selected from the group consisting of —H, —F, —Cl, —Br, —I, —NO 2 , —CN, —CF 3 , —R 1 , —OR 1 , aryl- and —O-aryl, R 7 is —H, —Cl, —Br, —I, -phenyl, —O-phenyl, —S-phenyl, —N(phenyl) 2 , -pyridyl, a barbituric acid radical or a dimedone radical, it also being possible for the phenyl radicals to be further substituted, R 8 and R 9 , independently of one another, are >C(CH 3 ) 2 , —O—, —S—, >NR 1 or —CH═CH—, and the anion Y m− has the general formula [AR 10 k ] m− with a polar, ionic head group A and k nonpolar groups R 10 , k is 1, 2 or 3 and m is 1 or 2, and the nonpolar groups R 10 , independently of one another, are at least one selected from the group consisting of linear, branched and cyclic alkyl groups having 6 to 30 carbon atoms and alkylaryl groups of the general formula -aryl-R 11 , where R 11 is a linear or branched alkyl group having 3 to 30 carbon atoms, or the anion Y m− is a borate anion of the general formulae (V) or (VI) where R 10 is as defined above and R 12 is at least one substituent selected from the group consisting of H and linear, cyclic and branched alkyl groups having 1 to 20 carbon atoms, and in the radicals R 10 , R 11 and R 12 , even nonneighboring carbon atoms may optionally be substituted by O atoms and/or the radicals R 10 , R 11 and R 12 may be completely or partly fluorinated, with the proviso that the nonpolar character of the groups is not substantially influenced thereby.