Patent ID: 8900414

Claim:
A process for preparing a marked fiber product comprising at least 20% by weight of cellulose fibers, based on the weight of the anhydrous fiber product, comprising the steps of i) incorporating into the body of the fiber product a) 1% to 10% by weight, based on 100% by weight of anhydrous fiber substrate, of at least one acid, that may be partially pre-neutralized with a base, wherein the acid is selected from at least one of polyphosphoric acid, phytic acid, diethylenetriamine penta(methylenephosphonic acid), hexamethylenediamine tetra(methylene-phosphonic acid), nitrilotris(methylene phosphonic acid), 1-hydroxyethyl(id)ene-1,1-diphosphonic acid, amino-tri(methylene) phosphonic acid, ethylene diamine tetra-(methylene) phosphonic acid, 2-phosphono-1,2,4-butanetricarboxylic acid, 2-(4-aminophenyl)-6-methylbenzothiazole-7-sulfonic acid, and abietic acid, wherein the proton in the OH group of the at least one acid may be at least partially replaced by ammonium or a protonated amine, and b) 0.3% to 7% by weight, based on 100% by weight of anhydrous fiber substrate, of a cationic retention aid, and ii) exposing those parts of the resulting fiber product, where a marking is intended, to energy by means of a laser beam, wherein the fiber product exhibits stronger marks in comparison with a fiber product not treated with said acid and retention aid when exposed to a laser beam.