Direct light fast dye is a powdered dye.

Characteristics of direct light fast dyes

Direct dyes contain water-soluble groups, and their solubility significantly increases with increasing temperature. For direct dyes with poor solubility, pure alkali can be added to assist in dissolution. Direct dyes must be dissolved in soft water. If the hardness of dyeing water in production is relatively high, pure alkali or sodium hexametaphosphate can be added, which is beneficial for dye dissolution and has the effect of softening the water.

Direct dyes have higher directness towards cellulose fibers than other dyes. At the same time, direct dye molecules contain groups such as amino, hydroxyl, and azo groups, which can form hydrogen bonds with hydroxyl groups in cellulose fibers and amino groups in protein fibers, further improving the directness of the dye.

When dyeing cellulose fibers with direct dyes, salt plays a dyeing promoting role. The dyeing promotion effect of different direct dye salts varies. The salt effect of direct dyes with more sulfonic acid groups in the molecule is significant. When promoting dyeing, the salt should be added in batches to ensure uniform dye uptake. Direct dyes with low dye uptake require the addition of more salt, and the specific amount can be determined based on the type of dye and dyeing depth. Light colored products with high requirements for levelness should reduce the amount of salt appropriately to avoid local uneven dyeing and dyeing defects such as color spots.

Operation process of direct light fast dyes

A impregnation

Dip dyeing is a method of immersing a dye in a dye solution and gradually absorbing the dye into the fibers through a certain dyeing process to achieve the dyeing goal. This dyeing method does not require high equipment requirements and can be operated manually or mechanically, without being limited by the tissue and quantity of the dye. It is now described below.

1、 Dip dyeing of cotton hank yarn

Since the application of dyes such as reduction, insoluble azo, and sulfide with good dyeing fastness in the dyeing of cotton skein with direct dyes, their use has gradually decreased. However, certain colors (such as black) still retain the advantages of direct dyes, with reduced dyes having poor blackness. Although sulfide dyes can achieve a certain blackness, the dye is prone to brittleness when placed. Direct dye dyeing can meet the requirements of black without the disadvantage of brittleness. In addition, due to the low requirements for color fastness in certain dyeing products, and the simpler and lower cost of direct dyeing methods, direct diazo black dyes are also used for yarn soaking in certain situations.

2、 Dip dyeing process of viscose twisted yarn

Twisting preparation → dyeing → washing → dehydration → fixation → oiling → dehydration → drying.

3、 Dip dyeing process of mulberry twisted silk

Twist refining → water washing → dyeing → water washing → dehydration → fixation → water washing → oiling → dehydration → drying.

4、 Dip dyeing process of cotton knitted fabric

Grey fabric preparation → dyeing → washing with water → paraffin treatment → dehydration → drying.

5、 Dip dyeing of Qiaoqi Lirong

Qiaoqi Lirong is a plant made of viscose as the surface and silk as the ground, with the villi forming a W-shaped tissue. After dyeing, water repellent and pressure resistant finishing is usually used, hence it is also known as waterproof and pressure resistant pile. During the dyeing and finishing process, fabric subjected to heavy pressure, folding, friction, elongation, and other factors can affect the quality of the finished product. Therefore, using a vertical star frame dyeing machine for immersion dyeing is more appropriate.

6、 Dip dyeing of wool and viscose blended fabrics

There are two methods for dyeing wool viscose blended fabrics with direct dyes. One is to use dyes that can dye wool and viscose to the same color. Another method is to use direct dyes on wool fabric to dye viscose, leaving the wool white; Alternatively, wool can be dyed with acidic dyes first, followed by direct dye dyeing to achieve a dual color effect.

B roll dyeing

The application of direct dyes in roll dyeing of fabrics has its own advantages and disadvantages compared to dip dyeing. Although the penetration and fiber coverage of roll dyeing are not as good as rope dyeing, they are not as good as dyeing for the flatness of tight fabrics, especially for viscose silk fabrics. Using a loose roller dyeing machine for dyeing results in better results.

There are many varieties used for roll dyeing, mainly including cotton fabric, viscose fabric, viscose silk interwoven fabric, vinylon cotton or vinylon blended fabric, etc.

C pad dyeing

Direct dyes can be used not only for dip dyeing and roll dyeing, but also for pad dyeing, abbreviated as pad dyeing; And because the fabric after pad dyeing must be steamed and fixed, it is also known as the pad steaming method. The covering power of pad dyeing on fibers is the same as that of roll dyeing, not as good as that of rope dyeing, and pad dyeing is not uniform and transparent enough. In addition, due to the fact that some commonly used direct dye dyed viscose and silk fabrics are generally not suitable for pad dyeing, direct dyes are only used in small quantities for pad dyeing of cotton fabrics.