The factors influencing the dyeing of pulp

The factors influencing the dyeing of pulp

(Summary description)

1. Properties of pulp: various sizes have different coloring properties. Lignin has strong affinity for basic dyes and cellulose has strong affinity for direct dyes. Because of the different lignin content of different sizes in the mixed pulp, it is easy to produce color spots. Straw pulp is easier to dye than wood pulp; the pulp with high beating degree and good fiber sweeping can improve the retention rate of pigment, and the paper is compact and transparent, which is conducive to absorption spectrum and deepening color.
2. Influence of bauxite: the rubber material has a blocking effect on the absorption of dyes and fibers. After adding bauxite, it can play a role of mordant. Acid dyes have negative charge, so it is necessary to change the charge with bauxite, adsorb on the negatively charged fiber, and improve the retention rate of dyes. However, excessive bauxite will reduce the pH value of slurry to below 4.5, which is not good for basic dyes and direct dyes, darken the color phase, and weaken the ability to resist sunlight. For most dyes, when pH value is between 4.5-5.5, the retention rate is the highest and the coloring effect is the best, but when pH value is more than 5, the retention rate of acid dyes will decrease obviously.
3. Influence of residual chemicals: many oxidation and reduction substances remained in the pulp, as well as substances with high acidity and alkalinity will affect the dyeing depth and color. For example, Fuchsia, Congo red, etc. will turn dark blue in case of acid. Because common dyes are indicators and are most affected by oxidation and reduction agents, residual chlorine in bleached pulp must be cleaned. In addition, calcium salt has adverse effects on most dyes, so the production water, especially the melted dye, needs soft water.
4. Effect of fillers: fillers have strong affinity with dyes, even more than dyes absorbed by fibers. In particular, direct dye absorption is stronger. Therefore, when dyeing the paper pulp containing filler, some dyes are absorbed by the filler to make the color of the paper lighter or uneven. Therefore, the dye should be added before the filler. When using rosin gum or bauxite, the dye should be fixed on the fiber first, and then the filler should be added.
5. The influence of temperature: temperature has a great influence on the dyeing effect, especially for direct dyes, such as direct red 23, the coloring degree is only 26% at 20 ℃, and the coloring degree can be increased to more than 80% when the temperature is raised to 45 ℃.
6. Production conditions of paper machine: high speed of paper machine will reduce the retention effect of dyes. Too high temperature of drying cylinder will make some dyes fade or cause color spots. Therefore, pay special attention to the temperature control of drying cylinder in the production of color paper.
In addition, after calendering, the color of dyed paper becomes darker and more obvious when the water content is large. For example, in the production of colored translucent paper, after wet overpressure treatment, the color is very bright.
Application Department of Yadong company
Wang Liping

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