Process for stabilizing the whiteness of lignin-containing fibrous materials, stabilizer composition and fibrous materials stabilized with this

Abstract

Lignin-containing fibrous materials, in particular paper and card, are treated with whiteness stabilizers for the purpose of reducing light-induced yellowing. The whiteness stabilizer are (i) thiols with at least one additional hydrophilic group from the series consisting of OH, NH2, NHR1m NR1R2, COOH, SO3H and PO3H2 and an amino acid / peptide structure (ii) thiols with a CC double bond (iii) or heteroaromatic thiols and (iv), heteroaromatic disulfides or polysulfides. HALS light stabilizers and / or UV stabilizers are advantageously additionally employed. The stability is increased further by a TiO2-containing coat on the fibrous material. Stabilzer compositions and fibrous material stabilized according to the invention, containing a whiteness stabilizer of group (i) to (iv) are also disclosed.

Description

INTRODUCTION AND BACKGROUND[0001] The present invention relates to a process for stabilizing the whiteness of lignin-containing fibrous materials, in particular paper and cardboard of mechanically produced fibrous materials, in particular wood pulp, against light-induced yellowing. The process comprises the use of a sulfur-containing whiteness stabilizer. The invention furthermore relates to whiteness-stabilized lignin-containing fibrous materials obtainable according to the invention and to a stabilizer composition.[0002] The low stability to whiteness of lignin-containing high-yield fibrous materials such as are obtainable using mechanically produced fibrous substances, that is to say in particular fibrous substances produced thermomechanically (TMP), chemo-thermomechanically (CTMP) or by stone-grinding of wood (SGW), is a serious obstacle to employing high-yield fibrous substances obtained in this way, in particular wood pulps, for the production of high-finish paper and card pro...

AI Technical Summary

Benefits of technology

[0021] According to the invention, the resistance to yellowing of lignin-containing fibrous substances and the materials produced therefrom can be increased and the whiteness thus stabilized if a thiol compound according to the invention is employed in an active amount during the production of the fibrous material. The amount employed depends on the desired degree of stabilization and on whether and to what extent further whiteness stabilizers and / or co-additives are employed in the production of the fibrous material. The amount of thio compound according to the invention employed is conventionally in the range from 0.01 to 5 wt. %, preferably 0.1 to 3 wt. % and particularly preferably 0.5 to 2 wt. %, in each case based on the dry fibrous substance.

Problems solved by technology

The low stability to whiteness of lignin-containing high-yield fibrous materials such as are obtainable using mechanically produced fibrous substances, that is to say in particular fibrous substances produced thermomechanically (TMP), chemo-thermomechanically (CTMP) or by stone-grinding of wood (SGW), is a serious obstacle to employing high-yield fibrous substances obtained in this way, in particular wood pulps, for the production of high-finish paper and card products.

Bleached lignin-containing wood pulps and celluloses in particular are highly susceptible to light-induced yellowing.

A disadvantage of thioglycerol is its low molecular weight and therefore also its unpleasant smell, which impedes use in practice.

It is stated in WO 99 / 05108 that the substances mentioned in this document are still not an adequate and practically applicable solution for avoiding light-induced yellowing.

The high amount of the said bisthiols employed is a disadvantage of this process.

Images