Method for treating cellulose-containing fibers or planar structures containing cellulose-containing fibers

The invention relates to a method for treating cellulose-containing fibers or planar structures containing cellulose-containing fibers.

US 2004/0118540 A1 describes a papermaking process in which first a high molecular weight amine component having an NH₂ concentration of at least 1.5 meq/g is introduced into the aqueous cellulose fiber mixture. Separately therefrom, a second component which can react with amino groups and which is either a polyanionic compound or an aldehyde-functional polymer is then added.

A paper product having increased strength is claimed in U.S. Pat. No. 6,824,650 B2. The product contains a combination of a polyvinylamine and a complexing agent selected from an aldehyde-functional polymer and a polyelectrolyte. The paper product is strengthened by reaction of polyvinylamine with the complexing agent.

Articles which contain cellulose of which at least part was chemically modified and where a further chemical has formed chemical bonds are claimed in U.S. Pat. No. 6,916,402 B2. The chemical modification of the cellulose can be carried out with compounds which contain aldehyde, epoxy or anhydride groups, while the further chemical then contains amino, thiol, amido, sulfonamide or sulfinic acid groups—or vice versa.

It was the object to provide a method by means of which the wet strength of cellulose-containing products, in particular the wet strength of paper towels, is to be increased, it being intended that the products also have a soft handle. The object is achieved by the invention.

The invention relates to a method for treating cellulose-containing fibers or planar structures containing cellulose-containing fibers with a combination of

(1) compounds having at least two primary amino groups and
(2) compounds having at least one β-ketocarbonyl group.

The compounds (1) used in the method according to the invention may have a monomeric, oligomeric or polymeric character. The compounds (1) preferably contain at least five primary amino groups (—NH₂), preferably at least 20 primary amino groups (—NH₂) and particularly preferably at least 100 primary amino groups (—NH₂). The density of amino groups in compounds (1) is preferably at least 1.0 meq/g, preferably at least 3.0 meq/g (meq/g=milliequivalent per g of substance=equivalent per kg of substance).

Polyamines are preferably used as compounds (1). Examples of compounds (1) are polymers of ethyleneimine in linear or branched form and polyvinylamine. The latter obtained by polymerization of N-vinylformamide and subsequent partial or complete hydrolysis are generally commercially available in the form of aqueous dilutions.

The compounds (2) used in the method according to the invention may have a monomeric, oligomeric or polymeric character, preferably a polymeric character. The compounds (2) preferably contain at least two β-keto-carbonyl groups and preferably at least three β-keto-carbonyl groups.

The β-ketocarbonyl groups in compound (2) preferably have the structure of the formula

—Y′—C(O)—CHR⁴—C(O)—CH₂R⁴

or its tautomeric enol form of the formula

—Y′—C(O)—CR⁴═C(CH₂R⁴)—OH