| abstract |
Process for the production of optionally wood-containing cellulose-containing sheet-like structures, such as paper, pasteboard and card, which have been given a dry strength and/or wet strength treatment and have improved whiteness, using water-dispersible isocyanates, wherein the water-dispersible isocyanates: a) are aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an NCO functionality of 1.8 to 4.2, mixed with polyether-modified aliphatic, cycloaliphatic, araliphatic or aromatic isocyanates having an average NCO functionality of 0.8 to 3.2, b) the isocyanate mixtures a) contain 1 to 25% by weight of isocyanate groups, c) have a content of ethylene oxide units, arranged in the form of polyether chains of average molecular weight 10 to 3500 (number-average), of 20 to 60% by weight, based on the isocyanate mixture, and if appropriate d) have a content of tertiary amino groups and/or ammonium groups of 1 to 500 milliequivalents per 100 g of isocyanate mixture a). |