Methods for improving discoloration resistance of pulp and pulp improved in discoloration resistance

Abstract

The present invention aims to provide a method for improving discoloration in pulp, characterized by a versatile technique adaptable to any type of pulp, a time-saving process, a great and permanent anti-fading effect, environmental friendliness and other properties, as well as a pulp with greatly improved discoloration obtained by said method for improving discoloration. Discoloration in pulp can be greatly improved by adding one or more additives selected from the group consisting of reducing agents, peroxides and hydrogen-donating organic compounds to one of bleached mechanical pulp, semi-chemical pulps, chemical pulp and deinked pulps or a mixture of two or more of them, and irradiating it with UV and / or visible light.

Description

TECHNICAL FIELD [0001] The present invention relates to methods for improving discoloration in pulp, more specifically to novel methods for improving discoloration in pulp using specific compounds, and to pulp with improved discoloration prepared by the methods for improving discoloration. PRIOR ART [0002] Brightness loss or discoloration in pulp over time is a common issue for any type of pulp including chemical pulp (hereinafter referred to as CP) such as KP, AP, SP; semi-chemical pulp (hereinafter referred to as SCP); mechanical pulp (hereinafter referred to as MP) such as SGP, RGP, PGW, TMP, CTMP, BCTMP; and deinked pulp (hereinafter referred to as DIP). The extent of discoloration in pulp is mainly influenced by the residual amount of lignin or modified lignin in the pulp, and discoloration tends to advance as the residual amount of lignin or modified lignin increases. Thus, discoloration advances the most rapidly in MP characterized by low degrees of bleaching, followed by SCP...

AI Technical Summary

Benefits of technology

[0017] and other properties, as well as a pulp with greatly improved discoloration obtained by said method for improving discoloration.

[0018] Discoloration in pulp can be greatly improved by adding one or more additives selected from the group consisting of reducing agents, peroxides and hydrogen-donating organic compounds to one of bleached CP, SCP, MP and DIP or a mixture of two or more of them and irradiating it with UV and / or visible light.

Problems solved by technology

In this method, however, large amounts of chemicals or the like must be used to degrade / remove lignin and these treatments cause problems such as yield losses in bleached pulp or strength losses in pulp fibers.

Large amounts of acids are required to remove hexenuronic acid, which also invites the problem of strength losses in pulp fibers.

However, MP are mainly used for mechanical paper and newsprint papers due to the problem of significant discoloration, and are only partially used for applications requiring high brightness and long shelf life such as printing paper and recording paper at present.

However, UV absorbents or the like have a disadvantage in that their effect does not continue for a long period because they are deteriorated by UV light.

On the other hand, when a rhodium catalyst was used for reducing the lignin aromatic ring, it took such a long period as 5 days to partially hydrogenate the aromatic ring in the hydrogenation reaction of the aromatic ring of the lignin isolated from wood at room temperature in an aqueous alcohol solution, and this catalyst seems very difficult to directly react with the lignin present in pulp fibers because it is used as an emulsion.

Thus, all of these conventional methods have disadvantages such as insufficient anti-fading effect, long processing time, lack of economy or practicability, etc. at present.

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