What are the characteristics and processes of yarn dyeing?

Compared to fabric dyeing, yarn dyeing requires ensuring that the dye penetrates the entire yarn bundle, achieving uniform color throughout the inner and outer layers, and avoiding "white cores" or color variations. The basic process is as follows:

Pretreatment:

Acrylic yarn typically contains spin oils and impurities and must be scoured and washed to ensure good wettability for subsequent uniform dyeing.

Yarn Loading:

The yarn is loaded into the dyeing equipment (e.g., a cheese dyeing machine or a hank dyeing machine). The density and uniformity of the yarn loading are crucial to ensure that the dye liquor flows evenly and smoothly through each yarn.

Dyeing:

The treated yarn is placed in a low-temperature (50-60°C) dye bath containing dyeing chemicals (dye, retarder, pH adjuster, etc.). The dye circulates for a period of time to achieve initial uniform dye absorption.

Heating:

The temperature is slowly raised to the boiling point (100°C) at a carefully controlled rate (e.g., 1°C/minute). This is the most critical step. Slow heating is crucial for ensuring even dyeing, allowing the dye time to diffuse evenly from the fiber surface into the interior.

Hot Holding:

The yarn is held at boiling temperature for 45-60 minutes to ensure the dye is fully set and complete the dyeing process.

Post-Processing:

Cooling: The yarn is cooled slowly to prevent sudden cooling that can cause stiffening or wrinkling.

Washing: Removes loose color and improves color fastness.

Softening: Acrylic yarn may feel stiff after dyeing and often requires softening to restore its bulk and softness.