New Eco-friendly Method for Paper Dyeing
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For economical and environmental reasons, the paper industry has shifted the production of paper products towards dyed products made from pulp grades with a high content of recovered paper. The basic method for dyeing paper products is pulp colouring with direct and basic dyes. Disadvantages of this method include coloured white water and so-called „bleeding” processes when using those products. „Bleeding” processes are undesired when using tissue products. A new eco-friendly method for dyeing pulp with adducts of reactive dyes and selected cationic aliphatic polyamine compouds was developed. A reactive dye is added to refined pulp and then a cationic polyamine compound. The dyeing substance is adsorbed on the entire surface of refined cellulose based semi finished products in a water medium with a pH near to neutral. After web consolidation, an uniform dye penetrated paper product is obtained, with high colour life and strength. Reactive dyes contain 3’-carboxypyridine-1,3,5-triazine systems that react with cellulose in a medium near to neutral and at a temperature similar to web drying. As polyamine compounds, polycondensates of guanidine with hexamethylene-1.6-diamine and octamethylene-1,8-diamine were used. As was proved by a test done on coloured paper, these compounds are characterised by bactericidal and fungicidal properties, which are advised for tissue paper. The polyamine compounds mentioned cause the quantitative adsorption of dyes on cellulose based pulp, increasing the retention of cellulose fibre fines, and the white water is practically colourless. In principle, this dyeing method does not change the strength, optical, structural and dimensional properties of selected paper products.