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AssigneeBASF SE
InventorsKlaus Flory, Andreas Stange, Michael Kroener, Norbert Sendhoff
Estimating the term…
Cationic urea/formaldehyde resins are obtainable by condensing urea and formaldehyde in a molar ratio of from 1:1.5 to 1:3 in the presence of polymers which contain not less than 1 mol % of polymerized vinylamine units and have Fikentscher K values of from 5 to 300, in an amount of from 5 to 50 g per mole of urea in the end product, where the mixture is first a) precondensed at a pH of from 8 to 14, then acidified and b) condensed at a pH of from 1 to 5 until gel formation begins, c) then from 0.3 to 1.5 moles of formaldehyde are added per mole of urea used, d) post-condensation is carried out and e) the resin solution is subsequently neutralized. The resins thus obtained are used in papermaking as assistants for increasing the dry and wet strength of paper and result in less dulling of the whiteness of the paper.
A process for making paper having high dry and wet strength, which comprises adding to paper stock before sheet formation or applying to a surface of a paper sheet, a cationic urea/formaldehyde resin produced by condensing urea and formaldehyde in molar ratio of from 1:1.5 to 1:3 in the presence of polymers which contain not less than 1 mol % of polymerized vinylamine units and have K values of from 5 to 300 (determined according to H. Fikentscher in 5% strength aqueous sodium chloride solution at 25.degree. C. and at a polymer concentration of 1% by weight), in an amount of from 5 to 50 g, based on 1 mole of urea in the end product, where the mixture is first:
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