Technology | The influence and prevention of thermal migration of disperse dyes on the dyeing fastness of polyester
Heat treatment/fixing causes the disperse dyes to undergo a certain thermal migration, which has a significant impact on the dyeing quality of polyester fabrics (color fastness, vividness, shade, etc.); through the analysis of disperse dyes and dyeing process, heat treatment temperature and time, dye heat The effects of sublimation, surfactants and finishing agents, cleaning after dyeing, and heat setting process on the thermal migration of dyes will minimize the thermal migration of disperse dyes.
After the polyester fabric (pure polyester fabric or polyester-cotton, polyester-viscose and other interwoven/blended fabric) is dyed with disperse dyes (especially dyed with high temperature and high pressure for dark colors), it is subjected to dry heat treatment at a temperature above 130°C, such as heat tentering after dyeing. , Resin thermal baking, etc., the color fastness of dyed fabrics (such as soaping, rubbing, perspiration and sun exposure, etc.) usually changes to different degrees, generally medium and dark colors drop by 0.5 to 1.5; cloth shades occur to different degrees Change; the pollution of cotton/viscous components in polyester-cotton, polyester-viscose and other interwoven fabrics or blended fabrics will increase significantly.
Therefore, in the production of pure polyester fabrics (especially polyester elastic fabrics), polyester-cotton, polyester-viscose interwoven or blended fabrics, it often affects the color stability, color brightness and color fastness of dyed products to varying degrees, even Repair or downgrade the dyed product if it fails to meet customer requirements.
1. Cause Analysis
The thermal migration phenomenon of disperse dyes on polyester fabrics after dyeing is the key to the above problems. It means that when the dyed fabrics are finished at high temperature and shaped, part of the dyes migrate from the inside of the fiber to the surface of the fiber under the action of dry heat or humid air. Accumulation and redistribution on the fiber surface. Thermal migration is a redistribution phenomenon of disperse dyes in two-phase solvents (fibers and surface layer solvent additives). It is an inherent physical property and also causes the color fastness (wet fastness) of polyester-containing fabrics during dry heat treatment after dyeing. , Perspiration and rubbing fastness) decline and shade variation and other key factors such as fiber staining.
The thermal migration of disperse dyes is not absolutely under dry heat conditions, but also occurs during long-term storage. Since this thermal migration is mainly related to the structure of the disperse dye itself, the thermal migration of disperse dyes with different structures is also different, and the differences are also large; at the same time, all the additives that can dissolve the disperse dyes, including the high temperature of finishing Use soft finishing agent (silicone oil, antistatic agent and spinning oil) when setting the shape. When these auxiliaries are adsorbed on the fabric surface, they can accelerate the heat migration of disperse dyes, thereby giving the disperse dyes on polyester dyed fabrics. Hidden dangers and hazards that are difficult to overcome.
2. Mechanism discussion
A unique feature of disperse dyes is “thermal sublimation”. When the dye is sublimated from a solid state to a gaseous state, the dye changes from a solid macromolecule to a free and free monomolecular state. The free movement of monomolecular dyes is compared with that of macromolecules. The dye group is much easier; in addition, there are a large number of group structures similar to the molecular structure of the dye in the printing and dyeing processing aids. The molecules form an extraction effect, so that the dye molecules migrate from the fabric to the surface.
Since the dyeing principle of polyester fiber is different from other dyes, the sublimation fastness of disperse dyes can indirectly reflect the heat migration resistance of disperse dyes to a certain extent. The sublimation fastness of disperse dyes is not good. In the dry heat state, the solid state dyes are easily detached directly from the fiber in a gaseous state. The thermal migration process of disperse dyes can be explained as follows:
(1) In the process of high temperature dyeing, the structure of polyester fiber becomes loose, disperse dye diffuses from the surface of the fiber into the inside of the fiber, and mainly acts on the polyester fiber with hydrogen bond, dipole attraction and van der Waals force.
(2) When the dyed polyester fiber is subjected to high temperature heat treatment, the heat energy gives the polyester long chain higher activity energy, which intensifies the vibration of the molecular chain, and the microstructure of the fiber relaxes again, resulting in some of the dye molecules and the polyester long chain. The binding force is weakened. Therefore, some dye molecules with higher activity energy and higher degree of autonomy migrate from the inside of the fiber to the fiber surface layer with relatively loose structure and adhere to the surface of the fiber, forming a surface layer dye or adhering to other adjacent fiber components.
3. The main factors affecting the thermal migration of disperse dyes
(1) The relationship between fiber dyeing depth and thermal migration
Experiments show that there is a certain contrast between the dyeing depth of polyester fibers and the thermal migration of disperse dyes, that is, the deeper the color, the greater the thermal migration of the dye during high-temperature dry heat treatment, and the greater the impact on the dye quality. serious.
(2) The relationship between heat treatment temperature and thermal migration
Under normal conditions, the higher the temperature of dry heat treatment after polyester dyeing, the greater the thermal migration of the dye, and the more serious the effect on the color and fastness of the dyed product. Heat treatment below 130 ℃, the thermal migration of the dye is not great; heat treatment at 140 ℃ or even above 160 ℃, the thermal migration of disperse dyes is significantly increased. Because different disperse dyes have different thermal migration tendencies, the thermal migration of different disperse dyes is different when processed under the same dry heat condition. Therefore, the dyeing color matching formula should be reasonable, otherwise it will easily lead to changes in the color of the dyed product.
(3) The relationship between heat treatment time and thermal migration
The heat treatment (baking) time at the temperature of 180℃ is in the range of 20-40s. With the extension of time, the migration of the dye increases sharply; in the range of 40-50s, the thermal migration of the dye does not increase significantly; over 60s, low temperature and medium temperature On the contrary, the thermal migration of type disperse dyes decreases.
(4) The relationship between dye sublimation and thermal migration
There is a certain connection between the thermal sublimation and thermal migration of disperse dyes. It is imprecise to simply understand the thermal migration of dyes as thermal sublimation. Production practice has proved that some high-temperature dyes with good sublimation resistance have low thermal migration (such as disperse gray S-BN), and some have high thermal migration (such as disperse red S-3GFL, disperse dark blue HGL, etc.) ; Some low-temperature and medium-temperature dyes with poor sublimation resistance (such as Disperse Red B, Furong Brilliant Red E-RLN, etc.), based on the results of parallel determination, have little thermal migration.
Of course, the initiation temperature of the thermal migration of disperse dyes has a certain relationship with the sublimation resistance of the dye itself, that is, as the sublimation resistance of the dye increases, the initiation temperature of the thermal migration also increases accordingly. For example, the temperature of low-energy disperse dyes is around 130℃, the temperature of medium-energy dyes is around 135-140℃, and the temperature of high-temperature dyes is around 140-145℃.
(5) The relationship between surfactants and thermal migration
Most of the surfactants on polyester fibers have a serious impact on the thermal migration of disperse dyes, and different types of surfactants have different effects on the thermal migration of dyes. The order of the effect of commonly used surfactants on the thermal migration of dyes is: diffusing agent NNO <detergent LS <wetting agent JFC <soaping <Remibon A <detergent 209 <high temperature leveling agent 10 <flat plus O. The degree of influence of the same surfactant on the thermal migration of the dye is closely related to its adhesion amount on the fiber, that is, the more the amount of surfactant adhesion on the fiber, the greater the effect.
(6) The relationship between finishing agent and thermal migration (resin finishing, soft finishing, etc.)
In the process of high-temperature finishing of the fabric with resin, if the baking time is prolonged, the amount of dye falling off the fabric will gradually increase, the amount of dye dissolved in the resin layer from the fiber will increase, and the amount of dye migrating to the surface of the resin layer will also increase. The corresponding increase will have a greater impact on the shade.
Commonly used softeners or other finishing agents also have an impact on the thermal migration of disperse dyes, which varies with different varieties. For example, cross-linked silicone softeners have little effect, while surfactants have a serious effect on silicone softeners. The degree of influence of various softeners on dye thermal migration also depends on the processing temperature; as the finishing temperature increases , Its influence is getting bigger and bigger.
(7) The relationship between dyeing method and thermal migration
Experiments show that polyester fabric dyed with disperse dyes, when heat treated at high temperature (above 130°C), part of the dye molecules migrate to the inside, and part of the dye molecules move from the inside of the fiber to the surface of the fiber or into the second phase solvent on the surface of the fiber; However, different dyeing methods have different directions of dye thermal migration. Because atmospheric pressure dyeing is light-colored ring dyeing, after high temperature dry heat treatment, there is almost no sign of thermal migration from the inside to the outside. The dye on the fiber surface has a concentration gradient and moves to the inside of the fiber. Migration or diffusion.
Hot melt dyeing dyes are distributed inside the fiber, and there is also a certain concentration gradient; while high temperature and high pressure dyeing has good penetrability, there is almost no gradient in the distribution of dyes inside the fiber, so during high temperature dry heat treatment, the dye only moves outwards in one direction , Has a greater impact on the color and fastness of dyed fabrics, especially deep to extra dark.
(8) The relationship between heat setting and thermal migration
The dyes dyed by the fixed and unshaped blanks have the same phenomenon of thermal migration of dyes during high-temperature dry heat treatment; the setting before dyeing has a certain inhibitory effect on the thermal migration of the dyed products in the dry heat treatment, but this inhibitory effect is related to It is directly related to the lighter color of the shaped blank from 10% to 15% (the lighter the color, the less the thermal migration of the dye). Therefore, polyester fabrics have a practical impact on the thermal migration of disperse dyes.
4. Prevention of color migration of disperse dyes
(1) Strengthen the pretreatment of polyester fabric
First of all, improve the dyeing and finishing process to fully reduce the crystallinity of the crystalline part of the fiber macromolecular structure and increase the crystallinity of the non-crystalline area, so that the crystallinity of the various areas inside the fiber tends to be consistent. After the dye enters the fiber, the The bonding between the fibers is more uniform. This not only improves the level of dyeing, but also improves the fastness of dyeing to heat migration. If the crystallinity of each part of the fiber is not balanced enough, most of the dye stays in the amorphous area with a relatively loose structure, then after the extreme state of the external conditions, the dye is more likely to be separated from the amorphous area inside the fiber and migrate to the surface of the fabric. , Thereby reducing the color fastness of textiles. The pre-shrinking and pre-sizing of polyester fabrics (especially polyester elastic fabrics) are all processing steps to balance the crystallinity of the fibers. After processing, the dyeing depth and color fastness of the fabric can be improved.
Secondly, strengthen the pre-treatment of polyester fabric-refining and degreasing process. Some auxiliaries left on the polyester fiber before dyeing, such as surfactants that dissolve disperse dyes, such as antistatic agents and lubricants added during spinning and weaving, should be removed before dyeing to reduce The influence of dyeing and the harm of disperse dyes’ thermal migration phenomenon.
(2) Choose disperse dyes with low thermal migration and similar properties
It is necessary to choose disperse dyes with low thermal migration. Because the molecular weight of these dye structures is relatively large, the basic structure of the dye is similar or similar to the fiber structure, and the affinity with polyester fiber is also large, so it is relatively difficult to migrate from the fiber to the surface. It can improve the heat migration color fastness of polyester textiles.
Because different disperse dyes have different thermal migration tendencies, the thermal migration will be quite different when processed under the same dry heat conditions; the selection of color matching dyes should be the same type or high-energy dyes, because different types of dyes have thermal migration The ratio is different, and the corresponding sublimation fastness is also different. The sublimation fastness of high-energy disperse dyes is generally higher. Although the thermal migration fastness of the dye is not consistent with the sublimation fastness, the high-temperature dyes have less dye sublimation under higher temperature setting, and the corresponding shade stability is also better.
(3) Additive selection of dyeing depth and dye compatibility
Because the color depth has a significant effect on the thermal migration of the dye, try to avoid reaching or even exceeding the saturation value of the dye during dyeing. When selecting dyes, it is necessary to consider not only the thermal migration of the dye itself, but also the advantages and disadvantages of its lifting power and dyeing compatibility.
(4) Strengthen the reduction and cleaning after dyeing
The dye (floating color) attached to the fiber surface will aggravate the thermal migration of the dye and affect the color fastness of the dyed fabric. It is necessary to strengthen the reduction cleaning after dyeing (adding auxiliary agents that are conducive to reduction cleaning), especially for deep to special dark colors. Sufficient reduction and cleaning to completely remove dyeing floating color and auxiliary agents used in the dyeing process.
(5) The influence of finishing agents and other additives on the color fastness
Since the commonly used softening finishing agents or other finishing agents mostly affect the thermal migration of disperse dyes, the finishing agent must be selected reasonably when finishing (softening or functional finishing) of polyester dyed fabrics. For the softener used in polyester fabrics, the softness, smoothness, yellowing, color change, and the effect on dye thermal migration must be considered at the same time.
(6) Polyester fixing treatment after dyeing
During the high temperature setting process of polyester fabric disperse dyes, part of the dyes inside the fiber migrate to the surface of the fiber. The dyes migrated on the surface of the fabric will reduce the color fastness to washing, dry/wet rubbing fastness and sublimation fastness, etc. Light colors, sensitive colors with multiple dye combinations are prone to color change. The treatment with the new polyester fixing agent Untrafix ECT can isolate the migration channel of dye monomolecules, reduce the influence of thermal migration of disperse dyes on the color fastness of dyed fabrics, and effectively improve its heat migration and various color fastnesses.
(7) Use a gentler process for finishing
The deeper the dyeing depth of polyester fabric, the higher the heat treatment temperature after finishing, the greater the impact on dye migration. Under the circumstance of ensuring the finalization effect of textiles, the final setting temperature should be lowered as appropriate depending on the variety, so as to avoid or reduce the migration of disperse dyes, which can significantly improve the color fastness of the fabric. For this reason, when finishing polyester fabrics after dyeing with disperse dyes, high-temperature pre-dyeing can be used as much as possible, and the finished product after dyeing should adopt milder process conditions.
5. Concluding remarks
5.1 The thermal migration of disperse dyes is the redistribution of the dye in the two phases of the fiber and the surface solvent. It is a key factor that causes the color fastness of polyester fabrics to decrease and the color and light variation during the heat treatment after dyeing. , Color and light stability) have a greater impact. In actual production, it is necessary to strictly master the dyeing and finishing process, select disperse dyes, dyeing and finishing auxiliaries, strengthen reduction cleaning, and reasonably formulate pre-treatment and post-finishing processes, so as to control the thermal migration of disperse dyes to a minimum.
5.2 There is a certain connection between the thermal sublimation and thermal migration of disperse dyes, but they should not be confused with each other as the same concept; because different disperse dyes have different thermal migration tendency, they will be treated under the same dry heat condition. The difference in the amount of heat migration will also lead to changes in the shade of polyester dyes and the staining of other fiber components in the blended fabric.