Cellulose ethers with delayed solubility and having a reduced glyoxal content

A process for producing cellulose derivatives reversibly crosslinked with glyoxal and thus having delayed water-solubility, comprising the steps of:

• a) providing a water-moist cellulose derivative,
• b) providing an aqueous solution comprising glyoxal, one or more alkaline earth metal salts and/or alkali metal salts of phosphoric acid as buffer substance,
• c) mixing the aqueous solution from b) with the cellulose derivative from a) at a temperature between 20 to 70° C. to achieve reversible crosslinking of the cellulose derivative,
• d) drying the reversibly crosslinked cellulose derivative and
• e) grinding the cellulose derivative,
• where steps d) and e) may be combined into a grinding-drying operation,
• wherein the aqueous solution as per b) comprises an organic acid having a basicity of one or more, where a monobasic, dibasic, tribasic or polybasic organic acid is present in an amount of 0.002 to 0.015 mol and the glyoxal is present in an amount of 0.010 to 0.050 mol, in each case per mole of anhydroglucose units of the cellulose derivative,
• the monobasic organic acid to glyoxal molar ratio is in the range from 1:1 to 1:6, the dibasic organic acid to glyoxal molar ratio is in the range from 1:1 to 1:10, and the tribasic organic acid to glyoxal molar ratio is in the range from 1:2 to 1:12.