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US 5,902,454 AGranted
Method of whitening lignin-containing paper pulps
AssigneeCiba Specialty Chemicals Corporation
InventorRandall B. Nelson
Life of this patent
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Abstract
A process to increase the whiteness of paper made from a lignin-containing pulp is disclosed which comprises adding to an aqueous slurry comprising a lignin-containing pulp, in the paper making step, an effective amount of a chelating agent to decrease the content of salts of iron and other heavy metals to 100 ppm or less by weight, based on the dry weight of the pulp, or adding to said aqueous slurry an effective amount of a fluorescent whitening agent, or both a) and b).
Claims37
A process to increase the whiteness of paper made from a pulp which contains 5% or more of lignin on a dry basis which comprises:
- a) adding to an aqueous slurry comprising said lignin-containing pulp, in a paper making step, an effective amount of a chelating agent to decrease the content of salts of iron and other heavy metals to 100 ppm or less by weight, based on the dry weight of the pulp, or
- b) adding to said aqueous slurry an effective whitening amount of a fluorescent whitening agent, or both a) and b).
Dependencies are inferred from the claim text.