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Factors Of Affecting Paper Pulp Dyeing

1.Properties of pulp: various sizes have different coloring properties. Lignin has strong affinity for alkaline dyes and cellulose has strong affinity for direct dyes; Due to the different lignin content of different sizes, color spots are easy to occur in mixed pulp. Straw pulp is easier to dye than wood pulp; The pulp with high beating degree and good fiber sweeping can improve the retention of pigment, and the paper is compact and has good light transmittance, which is conducive to absorption spectrum and deepening chromaticity.
2.Influence of bauxite: the rubber compound hinders the absorption of dyes and fibers. After adding bauxite, it can act as a mordant. The acid dye has a negative charge. It needs to change the charge with the help of bauxite and adsorb it on the negatively charged fiber to improve the retention rate of the dye; However, excessive bauxite will reduce the pH value of the slurry below 4.5, which is unfavorable to alkaline dyes and direct dyes, darken the hue and weaken the ability to resist sunlight. For most dyes, the pH value is between 4.5-5.5, the retention rate is the largest and the coloring effect is the best; However, when the pH value of acid dyes exceeds 5, the retention rate will decrease significantly.
3.Influence of residual chemical substances: many oxidation and reduction substances remaining in pulp, as well as acidic and alkaline substances will affect the depth and color of dyeing. For example, benzopurpurine and Congo red will turn dark blue in case of acid. Because ordinary dyes are indicators and are most affected by oxidation and reducing agents, the residual chlorine in bleached pulp must be cleaned. In addition, calcium salt has adverse effects on most dyes, so soft water should be used for production water, especially for melting dyes.
4.Influence of fillers: fillers have strong affinity with dyes, even more than the dyes absorbed by fibers. In particular, direct dye absorption is stronger. Therefore, when dyeing the pulp containing filler, some dyes are absorbed by the filler to make the color of the paper lighter or uneven. Therefore, the dyes should be added before the filler. With rosin gum or bauxite, the dyes should be fixed on the fiber first, and then the filler should be added.
5.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 increased to 45 ℃.
6.Production conditions of the paper machine: the high speed of the paper machine will reduce the retention effect of dyes. If the temperature of the dryer is too high, some dyes will fade or cause color spots. Therefore, special attention should be paid to the temperature control of the dryer in the production of colored paper.
In addition, the color of dyed paper becomes darker after calendering, which is more obvious when the moisture is large. For example, in the production of colored translucent paper, the color is very bright after wet overpressure treatment.

Post time: Feb-17-2022