In the paper production process, some color materials are often used to make the paper have the desired color. I

n order to obtain the paper in desired color, dyes are usually need to add to the pulp or applied to the surface of the paper.

This process is called dyeing or toning. Today we will introduce direct paper dyes used in the paper industry.

Direct dyes generally refer to molecules containing water-soluble groups (sulfonic acid groups or carboxyl groups) and hydroxyl or amino groups that can generate hydrogen bonds, soluble in water, dyes have affinity for fibers, and can be dyed directly without a mordant during dyeing.

A type of dyes on fibers, which are widely used for dyeing cellulose fibers, protein fibers and blended fabrics.

According to the chemical structure, direct dyes can be divided into azo type (mainly), stilbene type, phthalocyanine type and oxazine type. The dyeing of direct dyes is the dyeing of fibers by forming two or more hydrogen bonds and van der Waals forces. Direct dyes have a strong affinity with fibers and can dye fibers directly. Therefore, if it is not uniformly mixed with the slurry, uneven dyeing and stains will occur.

Direct dyes will condense with aluminum ions and sulfate ions and reduce the dyeing effect. Therefore, it should be added before adding alum during operation.

Direct dyes are generally not suitable for the dyeing of groundwood pulp, because groundwood pulp has high lignin content and poor absorption of direct dyes, so the dyeing color is lighter.

The coloring power and vividness of direct dyes are far inferior to that of basic dyes, but their heat resistance and light resistance are better than those of acid dyes and basic dyes. In order to strengthen the dyeing, basic dyes can be appropriately added after the direct dyes.

In some occasions, individual bright blue direct dyes can be used as paper brighteners, such as direct violet.

Direct dyes that are commonly used for paper dyeing include direct royal blue, direct sky blue, direct red brown, direct scarlet, direct red 28, direct yellow g, direct dark brown MM, direct black EX and so on.

Contact person: Miss Jessie Geng

Email:jessie@xcwychem.com

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