Disperse dye compatibility technology and dye selection principles

In order to improve the color and light stability, the prerequisites for improving the first-class dyeing rate are as follows: select a disperse dye compatibility combination that has the same or similar dyeing temperature, light fastness, hydrolysis stability, thermal migration and thermal cohesion. Polyester is dyed under high temperature and high pressure (130℃).

As we all know, the key is to achieve the stability of the dyeing shade and the high compatibility of the practical performance of each dye component. The so-called compatibility of dyes refers to the similarity and compatibility of the practical properties of different dyes. Good compatibility means similar practical performance and excellent compatibility. Even if there are certain differences in the dyeing process and materials, the impact on the color light will be relatively small. It is not easy to produce color difference during the dyeing process and the taking process.

However, disperse dyes with different structures have different practical properties. Therefore, when using disperse dyes we must pay attention to the selection of dye performance compatibility. Production practice has proven that when dyeing polyester with disperse dyes at high temperature (125-135°C), the following principles must be followed for the compatibility and combination of dyes.

Choose dyes with the same temperature type for compatibility

Among disperse dyes, dyes with different temperature types have greatly different practical properties and poor compatibility.

Dip dyeing temperature

The test results show that disperse dyes with different temperature types have different optimal temperatures for dyeing polyester due to the complexity of their molecular structures and different molecular weights.

Low temperature dye (E type): 125°C

Medium temperature type (SE type): 130°C

High-temperature dye (S type), 135°C (optimal dip dyeing temperature: the dyeing temperature with the highest color yield and best reproducibility)

When disperse dyes of different temperature types are dyed under high temperature conditions, their dye uptake rates have different dependencies on the dyeing temperature. If the actual dyeing temperature is too low or too high, it will cause differences in the dyeing rates of disperse dyes with different temperature types, causing color fluctuations.

For example, E-type and S-type dyes are mixed and dyed using the intermediate temperature of 130°C. If the dyeing temperature is high, the dye uptake rate of many S-type dyes will increase significantly, while the dye uptake rate of E-type dyes will not change much. If the dyeing temperature is low, the dye uptake rate of these S-type dyes will decrease significantly, while the dye uptake rate of E-type dyes will change less.

Therefore, the difference in actual dyeing temperature (generally caused by temperature detection errors) will inevitably lead to large color differences, unstable color and light, and poor reproducibility when enlarging small samples.

 

Insulation

Keeping time

Because low-temperature type (E-type) disperse dyes have a relatively simple molecular structure and a relatively small molecular weight, they diffuse easily into polyester and have a fast coloring rate. Therefore, the requirements for high temperature insulation dyeing time are lower. Even if the high temperature insulation dyeing time is relatively short, it is easy to achieve color balance and achieve level dyeing and through dyeing.

 

As for high-temperature (S-type) disperse dyes, due to their relatively complex molecular structure and relatively large molecular weight, their diffusion rate in polyester is slow even when dyed at 130°C. In order to achieve a dyeing balance, level dyeing, through dyeing, and good reproducibility, a relatively long high-temperature heat preservation dyeing time is required.

 

E-type and S-type dyes have different requirements for the length of high-temperature heat preservation dyeing time. When the two are mixed and dyed, if the high-temperature heat preservation dyeing time is insufficient (the S-type dye fails to fully reach the dyeing balance), it will not only cause obvious color difference, but also cause problems with poor leveling effect.

 

Temperature control range

 

When using disperse dyes to dye polyester under high temperature and pressure, especially when dyeing light colors with jet overflow ropes, because disperse dyes are dyed rapidly in the temperature rise range of 100 to 120°C, it is easy to produce “cloud-like flowers”. Therefore, temperature control dyeing is required in this temperature zone. The heating rate must be controlled to slow down the dyeing rate.

 

However, since E-type dyes are easier to dye than S-type dyes, the temperature control range of E-type dyes is relatively low. Experiments show that the temperature control area of E-type dye is 100~115℃, and the temperature control area of S-type dye is 105~120℃.

 

Obviously, when E-type dyes and S-type dyes are mixed for dyeing, if the temperature is controlled according to S-type dyes, E-type dyes (especially light colors) may produce unevenness. If the temperature is controlled according to E-type dyes, it is beneficial for S-type dyes to dye light colors. When dyeing medium to dark colors, since there is still a lot of dye remaining in the dye solution after 115°C, once the temperature rises quickly, uneven coloring may occur.

 

Therefore, three points should be paid attention to in actual dyeing:

 

First, try to use low-temperature (E-type) dye compatibility. The reason is that E-type dyes can be dyed at a lower temperature of 120 to 125°C, which consumes less energy and takes a shorter dyeing time. Moreover, the leveling and dyeing effects and dyeing reproducibility are also relatively good. Only sublimation fastness is poor.

 

Second, try to avoid mixing dyes with different temperature types, especially E-type and S-type dyes.

 

There are two main reasons: First, their requirements for process conditions are quite different. Fluctuations in process conditions can easily cause color differences and color blooms. Second, their sublimation fastnesses are different. During the high-temperature dry heat finishing process, due to the different sublimation fastnesses of the two dyes, color changes, color blooms and color differences will occur.

 

If we have to mix dyeing, we can only use low-temperature (E-type) and medium-temperature (SE-type) dyes. Because their requirements for process conditions are relatively close.

 

If high-temperature (S-type) dyes must be used for dyeing (where sublimation fastness is required to be high), only isothermal (S-type) dyes can be used for dyeing. Moreover, it is best to use ultra-high temperature (135℃) dyeing.

 

The reason is that increasing the dyeing temperature can significantly increase the color yield of S-type dyes, reduce dye loss, and reduce the burden of sewage treatment. Moreover, it can also improve the coverage of polyester defects by S-type dyes. At the same time, it will also speed up the diffusion speed of S-type dyes and shorten the high-temperature heat preservation dyeing time. It has no obvious impact on the elasticity and feel of polyester.

 

Third, disperse dyes have problems such as inconsistent names and unclassified temperature types. Therefore, we must use a sublimation fastness meter to conduct actual testing before use, and clearly classify the sublimation fastness of each dye in order to correctly select the compatibility.

 

2.Choose dyes with good alkali resistance and stability for compatibility.

 

Disperse dyes have a chemical stability problem when applied under high temperature (125°C ~ 135°C) conditions. Among them, acid resistance and stability are better. The pH value of the dye bath is in the range of 3 to 6, which has little impact on the dye uptake rate (color depth) and will not cause obvious color difference. However, the alkali resistance stability is poor. Under the conditions of high temperature (125°C ~ 135°C) and pH>6, many commonly used disperse dyes will undergo hydrolysis reactions, causing the color to become lighter and the color and light to change.

 

Although acid needs to be added to adjust the pH value of the dye bath before dyeing, many external factors will cause the pH value of the dye bath to rise during the dyeing process, exceeding the safe range of the process.

 

for example:

 

①The dyeing water quality is alkaline. The pH value is neutral before heating and alkaline after heating (100°C).

 

② Semi-finished products to be dyed (especially T/C, T/R fabrics) contain alkali.

 

③Dyeing auxiliaries (such as chelating dispersants, spreading agents, anti-wrinkle agents, leveling agents, etc.) and dyes also have pH issues.

 

The test results show that the pH value of the residual liquid after dyeing is often higher than the pH value set before dyeing. Before dyeing, even if the pH value of the dye bath is adjusted to the weakly acidic range of 4 to 5, it will still be affected by the alkaline substances brought in by water, fabrics, auxiliaries, and dyes during the temperature-raising dyeing process. This also causes it to be higher than the safe range of pH value, causing dyes with poor alkali resistance and stability to undergo hydrolysis to varying degrees.

 

Note: Experiments have proven that the safest pH range for commonly used disperse dyes is 4 to 5. When pH>6, the color depth of many disperse dyes will decrease. It can be seen that when using dyes with different alkali resistance stabilities, if the pH value of the dye bath is too high, significant color change and color difference will occur. The most typical example is disperse dye black.

Disperse black is a deep ternary blend of disperse dyes.

 

These two sets of deep ternary colors have problems with poor compatibility in terms of alkali resistance stability. The alkali resistance stability of dark blue S-3BG is much worse than that of yellow brown S-2RFL and ruby S-2GFL (or bright red S-3GFL). Therefore, when dyeing at high temperatures (130-135°C) and the pH value of the dye bath is >6, serious color differences will occur due to the hydrolysis of dark blue.

 

 

Experiments have shown that when dyes with good alkali resistance and stability are used for dyeing, the color obtained is obviously stable and the reproducibility is significantly better. Under normal conditions, even if the pH value of the dye bath fluctuates, serious color differences will not occur.

  1. Choose a dye combination with similar light fastness.

When dispersing dyes are used to dye polyester at high temperatures, in addition to the consistency of sublimation fastness (isothermal dye compatibility), the consistency of light fastness should also be considered when combining color combinations.

 

Polyester dyed with disperse dyes at high temperature, like other dye-matched dyeings, generally has a color-matching light fastness that is always equal to or even lower than the level of the dye with the lowest light fastness among the color-matching components. That is to say, in the color combination of dyes, as long as one dye with low light fastness is included, even if the amount is small, the light fastness of the dyed product will be low. For example: dye a “pickle color” with the same depth and color.

 

 

 

Combination 1: Although the main color (blue) and secondary color (orange) dyes have good light fastness, the secondary color (red) dye has poor light fastness, and the compatibility of the three dye components is poor. The light fastness of patch dyeing is still low.

 

Combination 2: Since the three dye components have good compatibility in light fastness, the light fastness of the dyed product is also good.

 

Therefore, when combining disperse dyes, no matter the main color, secondary color, or secondary color to adjust the color light, dyes with comparable light fastness should be used. Especially when dyeing export color sheets that require high light fastness, we need to pay more attention. This is because only when the light fastnesses of the color-blocking dyes are comparable to each other, the color change will be minimal during the light fastness test or administration process, and the light fastness will be better.

 

  1. Try to use dyes with low thermal migration for dyeing.

 

Thermal migration of disperse dyes on polyester is a common physical property of disperse dyes. The test results show that there are two key points that deserve special attention.

 

1: The thermal migration of disperse dyes and the sublimation of disperse dyes are two completely different concepts. Low-temperature type (E-type) dyes have high sublimability, which does not mean high thermal migration. High-temperature (S-type) dyes have low sublimation properties, which does not mean low thermal migration.

 

2: Disperse dyes with different structures have different thermal migration properties under high temperature and dry heat conditions.

 

This brings insurmountable hidden dangers to the practical quality of disperse dyes. During the process of high-temperature post-finishing (such as setting) of dyed goods, the thermal migration behavior of dyes will not only significantly reduce the wash fastness of dyed goods, but also significantly change the color and light of dyed goods due to the different amounts of thermal migration of different dyes. .

 

Therefore, we should attach great importance to the harm caused by the thermal migration of disperse dyes to dyeing quality and try to use dyes with less thermal migration for dyeing. This is very effective in stabilizing the shade of the cloth surface and improving the wet fastness of dyeing.

  1. Use dyes with low thermal cohesiveness for dyeing.

 

Thermal cohesion (crystallization) is a common physical phenomenon of disperse dyes in high-temperature (>100°C) dye baths. Dye molecules or dye particles that are free or dispersed in water will aggregate into new or larger dye crystals or dye aggregates during the process of heating, maintaining, and cooling.

The thermal cohesion (crystallization) properties of some disperse dyes are of the following three types:

  1. The aggregation (crystallization) is relatively small and the dispersion stability is good.
  2. The agglomeration (crystallization) is relatively large, but with the extension of high-temperature dyeing time, the dye gradually absorbs the dye, and the agglomeration (crystalization) produced in the early stage of dyeing can be basically “depolymerized”.
  3. Condensation (crystallization) is strong. Even if high-temperature leveling agent is applied and the high-temperature heat preservation dyeing time is extended, the degree of thermal condensation (crystallization) will not be significantly improved. For example, Disperse Orange G-SF (c. 1.044).

A: Dyeing defects will not be caused by agglomeration (crystallization). But there are very few varieties of such dyes.

B: Although it has greater aggregation (crystallization) property, it can be “depolymerized”. As long as an appropriate amount of high-temperature leveling agent is applied and the high-temperature insulation dyeing time is appropriately extended, quality problems such as color spots and stains due to agglomeration (crystallization) will generally not occur. There are many varieties of this type of dye.

C: It has high aggregation (crystallization) properties and cannot be “depolymerized”, so it cannot be used. There are fewer varieties of this type of dye.

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