• head_banner_01

Paper Dyes

  There are many kinds of dyes commonly used in paper industry and their basic characteristics, and the classification methods are also different. Different kinds of dyes have different dyeing properties due to their different structures. Natural dyes are used for early dyeing. Due to their weak dyeing power and easy to change color in the sun, natural dyes have been replaced by rapidly developing synthetic dyes in the paper industry. Synthetic dyes are widely used in modern paper industry due to their water solubility, strong dyeing power, convenient and simple dyeing operation. At present, the dyes commonly used in the paper industry mainly include Basic dyes, Acid dyes and Direct dyes.

1.1 Basic dyes Basic dyes are soluble in water and have strong coloring power. They are easy to color the fiber and have bright colors. They are most widely used in the paper industry. However, its light and heat resistance are extremely poor, and its resistance to acid, alkali and chloride ions is weak, so the finished product is easy to fade. Hard water and alkaline water should not be used to dissolve alkaline dyes, otherwise color spots will occur. Therefore, the usual method is to add 1% dilute acetic acid to adjust the pH value to 4.5~6.5, and then use it after dissolving at 60 ~70 . Alkaline dyes have different dyeing properties for different kinds of pulp and have great affinity for lignin. Therefore, it is easy to dye pulp with high lignin content, such as unbleached pulp and mechanical pulp, but the affinity for bleached pulp is weak. Therefore, pay attention to this characteristic when dyeing mixed pulp, especially bleached pulp and unbleached or mechanical pulp. Otherwise, the dyeing uniformity will be affected. Generally, the addition of basic dyes should be after the rubber compound and aluminum sulfate. The representative varieties of basic dyes include Basic Megenta, Basic Auramine O, Basic Victoria Blue B, Basic Chrysoidine, basic brown G, etc.

1.2 1.2 Acid dyes Acid dyes are very soluble in water, and the hardness of water and the temperature of pulp have little effect on the dyeing effect. Compared with basic dyes, its dyeing ability and color brightness are worse than those of basic dyes, but its light resistance and heat resistance are strong, and its resistance to acid, alkali and chloride ions is poor. Because of its strong negative group, it has little affinity for plant fibers. During dyeing, it is necessary to use alum as a mordant to make the dye stay on the fiber. Therefore, acid dyes must be added to the pulp before adding acid and alum, so that the pulp and fiber can be mixed evenly before adding rosin and alum. Its dyeing effect is best at pH value of 4-5, so acid dyes are generally not used for non-sizing paper. Based on the above characteristics, acid dyes can be dyed uniformly without color spots when dyeing the mixed pulp. The representative acid dyes used in paper dyeing include Acid Metanil Yellow G, Acid Orange II, Acid Scarlet 3R, Acid Scarlet GR, etc.

1.3 1.3 The solubility of direct dyes in water is worse than that of acid dyes. They are insoluble in cold water, but soluble in hot water above 50 . The hardness of water has a slight impact on direct dyes. Direct dyes have strong affinity with fibers and can dye fibers directly. Therefore, if it is mixed with the slurry unevenly, it will cause uneven dyeing and color spots. Because the direct dye will coagulate with aluminum ion and sulfate ion, reducing the dyeing effect, it should be added before adding alum during operation. However, it is worth noting that direct dyes are generally not suitable for the dyeing of ground wood pulp, because the lignin content of ground wood pulp is high, and the adsorption of direct dyes is poor, so the color phase of dyeing is relatively light. The dyeing power and brightness of direct dyes are far less than those of basic dyes, but their heat resistance and light fastness are better than those of acid dyes and basic dyes. In order to strengthen dyeing, basic dyes can be added after direct dyes. Common direct dyes include Direct lake Blue 5B, Direct Scarlet 4BS, Direct Brown MM, Direct Black EX, etc.


Post time: Mar-22-2023