The Impact of Disperse Dye Thermal Migration on Fabric Quality

In the textile dyeing and printing industry, especially in the processing of polyester and its blended fabrics, the phenomenon of disperse dye thermal migration is a common and troublesome problem. Many dyeing and printing companies have encountered this situation: the fabric color and shade appear perfectly normal after dyeing, but after subsequent finishing or prolonged storage, changes in color and shade occur, even leading to mottled or streaky color variations, and a decrease in various fastness properties. The "culprit" behind this is the thermal migration of disperse dyes. Today, let's delve deeper into the principles, effects, and solutions to this phenomenon.

I. What is the thermal migration of disperse dyes?

Thermal migration of disperse dyes refers to a physical phenomenon that occurs after dyeing polyester fibers. During high-temperature dry heat treatment (such as heat setting and resin finishing), the dyes that have already penetrated the fiber migrate from the interior of the fiber to the fiber surface.

Specifically, this process involves the migration of disperse dyes from the interior of the fiber to the fiber surface through the fiber capillaries under high-temperature conditions, resulting in the accumulation and redistribution of the dye on the fiber surface.

The essence of thermal migration is a redistribution phenomenon of disperse dyes in a two-phase solvent system (fiber and auxiliary agents). All auxiliary agents that can dissolve disperse dyes, regardless of their ionic type and chemical structure, can cause thermal migration. If a second-phasesolvent is not present, thermal migration cannot occur.

2.Principles of Thermal Migration

The thermal migration process can be broken down into two key stages:

1. Dye Dissolution Stage: Auxiliary agents on the outer layer of the fiber dissolve the dye at high temperatures. These auxiliary agents may come from:

Antistatic agents and lubricants added during spinning and weaving

Antistatic agents, penetrants, stain repellents, and softeners added during dyeing and finishing

2. Dye Migration Stage: The dye dissolved in the auxiliary agents moves from the interior of the fiber to the fiber surface under the influence of temperature and time, and then redistributes on the fiber surface.

It is worth noting that the phenomenon of thermal migration is not absolutely related to the sublimation fastness of the dye. It is an inherent physical characteristic of disperse dyes, and different disperse dyes with different structures exhibit varying degrees of thermal migration, with significant differences between them.

3.Serious Impact of Thermal Migration on Fabric Quality

Thermal migration can lead to a series of quality problems in textiles, mainly manifested in the following aspects:

1. Color change and uneven dyeing: The redistribution of dyes on the fiber surface can cause changes in color shade. When the auxiliaries are unevenly adsorbed on the fabric surface, patchy or streaky color variations may occur.

2. Reduced rubbing fastness: Since the dye migrates to the fiber surface, it is more easily removed during rubbing, leading to a significant decrease in rubbing fastness.

3. Reduced washing and perspiration fastness: Dyes that have migrated to the fiber surface are more easily detached from the fiber in a wet environment, resulting in poor washing and perspiration fastness.

4. Other fastness problems: This also includes problems such as reduced dry cleaning fastness and light fastness.

5. Staining problems: During ironing, dyes that have migrated to the fiber surface may stain other fabrics.

It is worth noting that these quality problems usually only become apparent in post-dyeing processes or even in the finished product stage, leading to increased rework rates and higher production costs.

4. Effective Countermeasures to Address Thermal Migration Problems

To address the challenges posed by thermal migration, we can take the following approaches:

(1). Correct Selection of Dyes

Choosing dyes with low thermal migration and high wash fastness is crucial. These dyes typically have larger molecular weights and a higher affinity for polyester fibers, making it difficult for them to migrate from the interior to the surface of the fiber even under high-temperature dry heat conditions above 150°C.  

Tiankun Chemical has launched three series of high-washing fastness products with excellent thermal migration properties. These are the TXF series, suitable for 100% polyester fabrics, an economical option currently selling well in markets such as Bangladesh and Peru; the KXF series, suitable for polyester-spandex fabrics, especially for sportswear; and the SWF series, the highest-end series, which fully meets the dyeing requirements of international apparel brands.

(2). Strictly control the pre-treatment and post-treatment processes.

Pre-treatment: All residual auxiliaries on the fibers must be completely removed before dyeing. A degreasing agent from the Sylic brand can be used.

Finshing: During post-dyeing treatment and finishing, carefully select the chemicals remaining on the fibers.  A self-emulsifying softener without emulsifiers should be used, instead of an emulsion-type softener.

(3). Optimized Finishing Process

While ensuring the desired shaping effect, a finishing temperature of 150℃ or lower can be used. The darker the color, the more carefully the temperature needs to be controlled.

Multiple measures should be employed, including high-temperature pre-setting before dyeing, non-contact hot air drying below 130℃, low-temperature softening and stretching processes, and low-temperature, slow-speed resin finishing.

(4). Enhance reduction cleaning

Especially for dark shades, the excess dye must be thoroughly washed off to ensure good colorfastness.

Acidic cleaning is preferred. If using an alkaline hydrosulfite process, neutralization is essential, as some dyes are sensitive to pH.

(5).Controlling the Use of Auxiliary Agents

The use of surfactants should adhere to the principle of "avoiding their use whenever possible, and using as little as possible when necessary." If their use is unavoidable, the type of surfactant should be carefully selected, and the wastewater should be treated to ensure cleanliness.

Non-ionic surfactants, in particular, are the main cause of dye migration during heat treatment.

5. Methods for Detecting Thermal Migration

The phenomenon of thermal migration can also be detected using scientific methods:

Dimethylformamide (DMF) can be used as a solvent.  The fabric is immersed in the solvent for 3 minutes. Any dye that has migrated to the fiber surface should detach into the dimethylformamide, while the dye within the fibers will not detach.

Alternatively, the amount of migration can be measured using a colorimetric method.  Again using dimethylformamide as the solvent, after treatment at boiling point for 5-10 minutes, all the dye on the fibers will detach.

Conclusion

The thermal migration of disperse dyes is a significant problem in the dyeing and finishing of polyester fabrics.  It not only affects the appearance of the product but also its intrinsic quality and performance during use. By comprehensively implementing measures such as selecting appropriate dyes, optimizing process parameters, strictly controlling the use of auxiliaries, and enhancing washing effectiveness, we can minimize the impact of thermal migration and produce high-quality polyester textiles.

If you want to know more details about High washing fastness disperse dyes ,please contact us :info@tiankunchemical.com