The mechanism of thermal aggregation (crystallization) of disperse dyes and its impact on dye quality were analyzed. The absorbance method was used to detect and classify the thermal agglomeration properties of commonly used domestic disperse dyes; the process factors affecting the thermal aggregation properties of dyes were pointed out.
The so-called thermal cohesion of disperse dyes means that when disperse dyes are dyed at high temperatures (>100°C), free dye molecules or dispersed dye particles re-aggregate to form new ones. or larger dye particles (crystals).
01 Thermal agglomeration mechanism
Dispersion There are three main reasons for the aggregation (crystallization) phenomenon of dyes during high-temperature dyeing:
First, the molecular structure of disperse dyes does not contain hydrophilic groups, so the solubility is extremely small. . For this reason, when the dye is commercialized, a dispersant must be added, and its dosage is half or more of the amount of dye. The purpose is to enable the dye particles to be evenly and stably dispersed in the water to facilitate dyeing. The dispersants added to domestic disperse dyes are mostly dispersant N, MF or CNF. They all have the problem that the higher the water temperature, the worse the dispersing ability. That is, the binding energy between dye particles and dispersant will weaken as the water temperature increases, causing the original dispersion stability to decrease.
Second, as the dyeing temperature increases, the activation energy of the dyes themselves increases, and the probability of collision with each other increases. Those dye particles with poor dispersion stability will re-aggregate to form new or larger dye aggregates.
Thirdly, during the cooling process of dyeing, the dye will be reduced in water temperature, which will cause the thermal vibration to weaken and the solubility to decrease, causing the dye to precipitate and cause secondary condensation.
02 Effect of thermal condensation on quality
The thermal cohesion of disperse dyes affects the quality of dye products, mainly in three aspects:
First, due to the tight structure of polyester fibers, even at high temperatures (130°C) It is also difficult for dye aggregates or grains to enter the fiber when dyed under such conditions. Dyes are often adsorbed on the fiber surface to form floating colors, which can easily cause uneven color absorption, reduce the purity of the color, and affect the dye fastness.
Secondly, if the dye aggregates adsorbed on the fiber surface fail to be fully deaggregated or smoothed out through dye transfer during heat preservation dyeing, varying degrees of color will be produced. Spots and blemishes.
Third, the sticky dye aggregates in the dye bath sometimes form tar-like objects with the fallen fiber scraps and dissolved oligomers. Once attached to the fabric, irreparable “tar spots” will form, making the dye lose value.
03 Detection of Thermal Condensation
3.1 Detection Method
3.1.1 Formula
Disperse dye/(g/L)2
Ice Acetic acid/(mL/L)0.5
3.1.2 Treatment
Put 100mL of the dye solution configured according to 3.1.1 into a stainless steel cup and place it in an infrared dyeing machine for heat treatment.
The dye liquor that has not been heat treated is also subjected to suction filtration.
3.1.3 Detection
Absorb heat-treated or non-heat-treated samples respectively 5 mL of filtered dye solution was diluted to 50 mL with water. Shake well and then pipet 1 mL into a colorimetric tube. Add 10 mL of acetone to dissolve it into a transparent dye solution. Use distilled water as a reference sample and use a 721N visible spectrophotometer (Shanghai Precision Science) Instrument Company) to detect the absorbance respectively. Calculate the thermal aggregation degree of dye according to formula (1):
Description:
① Disperse dye is a dispersion of dye particles, which scatters light and cannot be detected by the 721N visible spectrophotometer, so it must be dissolved with acetone to make it a transparent solution.
② Some domestic disperse dyes have uneven particle sizes, and some of the larger dye particles will also be filtered out by the filter paper. Therefore, dye liquor that has not been heat treated must also be filtered through filter paper, otherwise the test results will be affected.
③During high-temperature (>100℃) heat treatment, the dyes in the disperse dye dispersion will not only condense into large aggregates, but also produce crystal growth and secondary crystallization. Large dye crystals. Therefore, the measured thermal condensation degree of dye is actually a comprehensive parameter of the degree of condensation and crystallization of dye.
3.2 Test results
As shown in Table 1, the degree of thermal condensation of domestic disperse dyes in high-temperature dyeing varies greatly. Most dye varieties have a slight tendency of thermal aggregation, such as dispersed golden 5E-3R, etc.; some dye varieties have a strong tendency of thermal aggregation, such as dispersed ruby S-5BL, etc.; a few dye varieties have serious thermal aggregation, such as dispersed orange G-SF ( 73#) etc.
Different varieties of disperse dyes have different maximum temperature ranges for thermal condensation. Most dyes have the greatest thermal aggregation tendency at about 130°C; while some dyes, represented by dispersed deep blue S-3BG (79#), have the highest thermal aggregation tendency at around 110°C. As the temperature increases, their thermal aggregation tendency will decrease. Significantly smaller.
The length of high-temperature insulation dyeing time has a direct impact on the degree of thermal cohesion of disperse dyes. to mostFor disperse dyes, extending the high-temperature heat preservation dyeing time can reduce or significantly reduce the degree of thermal condensation. For example, when incubated at 130°C for 10 minutes, the thermal cohesion property of dispersed blue E-4R (56#) is 12.17%; and when incubated at 130°C for 40 minutes, it is 7.63%. The thermal cohesion property of dispersed deep blue S-3BG (79#) is 14.33% when incubated at 130°C for 10 minutes; and 9.14% when incubated at 130°C for 40 minutes.
Obviously, this is related to the depolymerization of some dye aggregates (or crystals) after extending the high-temperature heat preservation and dyeing time. However, for a few dyes (such as disperse orange G-SF73#), extending the high-temperature insulation dyeing time has little effect on reducing the degree of thermal condensation. Special attention should be paid to the fact that during actual dyeing, the heat preservation time at a high temperature of 130°C should be sufficient.
This is not only to achieve a true color balance and improve color reproducibility, but also to eliminate uneven color absorption during the heating stage through high-temperature dye transfer. With the extension of the holding time, the dye will continue to dye and the dye aggregates will gradually depolymerize, which will also have a significant positive effect on improving the level dyeing and dyeing effect and improving the dye fastness.
(4) The degree of thermal aggregation of disperse dyes is closely related to the application of high-temperature dispersed leveling agents. The test results confirm that the thermal cohesion properties of most commonly used disperse dyes can be significantly improved by adding 1-2g/L high-temperature dispersion leveling agent to the dye liquor. Moreover, dyeing defects such as rung marks and washboard marks caused by structural differences such as polyester fiber crystallinity can also be better covered. For example, the thermal aggregation degree of Dispersed Deep Blue S-3BG can be reduced from 9.14% to 4..21%; Dispersed Blue E-4R can be reduced from 7.63% to 0.37%. However, for a few dyes such as disperse orange G.SF, the addition of high-temperature leveling agent has little effect.
04 Conclusion
1. Commonly used The thermal condensation behavior of domestic disperse dyes during high-temperature and high-pressure dyeing processes can be summarized into three types: A, B, and C.
Type A dye itself has a small degree of thermal cohesion, and extending the high-temperature insulation dyeing time or applying a high-temperature dispersion leveling agent will not have a significant impact on the thermal cohesion. This type of dye accounts for the majority and in practical applications generally does not cause dyeing defects due to dye agglomeration, so it is most suitable for dip dyeing.
Type B dye itself has a greater or greater degree of thermal aggregation, but with the extension of high-temperature insulation dyeing time and the application of high-temperature dispersing leveling agents, the degree of thermal aggregation will become significant. become smaller, or even basically deagglomerate. For this type of dye, as long as the heating rate is correctly controlled, the high-temperature insulation dyeing time is sufficient, and an appropriate amount of high-temperature dispersing leveling agent is applied, quality problems such as uneven color, reduced fastness, and color spots and stains due to dye agglomeration will not usually occur. Therefore, exhaust dyeing can be used when dyeing woven fabrics, but cheese dyeing and beam dyeing should be used with caution.
Type C dye itself has a high degree of thermal aggregation. Even if the high-temperature insulation dyeing time is extended and a high-temperature dispersing leveling agent is applied, the degree of thermal aggregation will not be significantly improved. Obviously, this type of dye is not suitable for exhaust dyeing.
2. Thermal cohesion, like alkali resistance stability, is an important practical performance of disperse dyes and will affect dyeing. Quality causes many problems. Therefore, it is crucial to detect and select the thermal cohesion properties of commonly used disperse dyes.
3. High-temperature dispersion leveling agent can effectively reduce the cohesion of disperse dyes in high-temperature dye baths. Apply an appropriate amount (1-2g/L) high temperature dispersion leveling agent is necessary. </p
