In production, it is often encountered that the surface and color of polyester or polyester-containing fabrics are normal after dyeing, but the color and light are inconsistent after finishing in the next process, resulting in discoloration or partial discoloration. Spots, streaks, and reduced fastness may appear. Such problems may be repairable in minor cases, but may be difficult to meet in severe cases even after repairs. This will affect the normal production, delivery, quality, and efficiency of the factory. bring certain impact and losses.
The following are the causes and preventive measures. Briefly explained for reference.
Reasons for poor color fastness of polyester fabrics after shaping
Polyester has high color fastness requirements For customers, in the actual production process, the dyeing factory still cannot achieve the ideal color fastness after high-temperature and high-pressure dyeing, reduction cleaning, and high-temperature setting.
The reason is: Thermal migration of polyester after dyeing with disperse dyes is the key to the above problems. Thermal migration is a common problem with disperse dyes. performance. It refers to the migration of part of the dye from the interior of the fiber to the surface of the fiber through the fiber capillary due to the action of dry heat or hot and humid air during post-finishing and high-temperature setting, causing the accumulation and redistribution of the dye on the fiber surface. The presence of additives and surfactants includes Residues on the cloth will aggravate its occurrence.
Since this thermal migration is mainly related to the structure of the dye itself, and disperse dyes with different structures have different thermal migration properties, and the differences between them are also large, so it is especially important during post-finishing and high-temperature styling. When using silicone oil and antistatic, it contains a certain amount of surfactant , and when these additives are unevenly adsorbed on the cloth surface, including uneven PH on the cloth surface, a series of problems such as the above-mentioned so-called color bloom, color change, and decrease in fastness such as friction, washing, and staining will occur. This kind of The phenomenon often manifests as one or several coexistences, which brings insurmountable hidden dangers and hazards to the dyeing quality.
Treatment measures
First, choose disperse dyes with small and similar thermal migration properties, because The molecular weight of these dye structures is relatively large, and their affinity with polyester fibers is also relatively large, making it difficult for them to migrate from within the fiber to the surface.
Try to use the same type of color matching dyes.Type or high-temperature dye, because different types of dyes have different thermal migration ratios and different sublimation fastnesses. The high-temperature type has higher sublimation fastness. Although the thermal migration fastness of the dye is not consistent with the sublimation fastness, the high-temperature type When the dye is set at a higher temperature, the sublimation of the dye is less, and the stability of the corresponding color light is also better.
Post-finishing adopts a gentler process. The darker the color, the more the dye will migrate. The higher the temperature, the greater the impact on migration. To ensure In the case of setting effect, depending on the variety, a temperature of 150°C or lower can be used to avoid or reduce dye migration.
It is necessary to choose the finishing softener. Try to use hydrophilic silicone oil or self-emulsifying block silicone oil that does not contain emulsifiers, and this type of silicone oil has good stability. , low discoloration and yellowing, and can have a better preventive effect on dye migration.
Strengthen the restoration cleaning after dyeing, especially for dark colors. The floating color must be fully cleaned to ensure its own fastness. At the same time, try to use acidic cleaning. If When using the alkaline insurance powder process, it must be neutralized, because some dyes are more sensitive to pH, and some will turn blue to purple after high-temperature finishing when the pH is >6, and some of this color change is irreversible, and even Cannot be repaired.
Factors affecting color changes during styling
The design of the shaping process is set according to the state of the B/F fabric: width, weight, strength, and shrinkage. Among them, the ones that have a greater impact on color changes are as follows: several parameters.
1. Temperature
Resin: dark color: 170℃; light color (sensitive Color): 150℃
But resin: 150℃
Dry cloth: 130-160℃ is acceptable, subject to dry cloth
Temperature 100-150℃ has little effect on color, greater than 150℃ The higher the temperature, the greater the impact on the color.
2. Speed
Set according to the fabric structure and thickness, generally:
170℃ 14M/MIN (gram weight greater than 250GM)
170℃ 16M/MIN (gram weight 200-250GM)
170℃ 18M/MIN (gram weight less than 200GM)
If the cloth surface does not dry during actual operation, first check whether the machine is normal; if so Then notify the person in charge of the process to slow down the machine speed and make process changes. Under the same temperature, keep the cloth surface dry (0-6% moisture content) with a difference of 2- The influence of 3M/MIN on the cloth surface is negligible.
3. Circulating air
a> .Usually, Class II air is used to pass the resin. The thermal efficiency is higher than Class I, and the impact on the color is greater than Class I;
b>. However, the denser and thicker structures with resin must use Class II wind; the looser and unstable fabrics can use Class I wind. The final shape is subject to the dryness of the cloth, and the impact on the color at the same temperature can be ignored.
4. Materials
a>. Resin, catalyst and fiber react chemically and combine covalently, changing the molecular arrangement inside the fiber, which has a greater impact on the color change of the fabric;
b>. The greater the amount of resin and catalyst, the greater the impact on color, and conversely the impact will be reduced;
c>. The influence of soft oil on color is based on its own color and ionicity. Soft oil with a yellow appearance has a greater impact on the color of the cloth than soft oil with a clean and white appearance. Cationic soft oil (surfactant) is softer than non-ionic soft oil. Oil has a great influence on the color of the cloth.
In short, the higher the amount of resin and soft oil added to a post-finishing formula, the greater the impact on the color of the cloth surface; the smaller the amount of resin and soft oil, the smaller the impact on the color of the cloth surface. This is for It should be given priority during process design
5. Door width
When designing the shaping process, a more reasonable door width is determined based on the different fabric structures, the different needle numbers of the KN machine, and the influence of the PD cylinder type. The principle is to ensure that the warp and weft directions of the fabric are The shrinkage is relatively average (such as 6×6%, 7×7%)
Post-finishing and trial-fitting personnel should first inquire about the post-finishing and shaping process before doing trial trimming to ensure that the door width reaches Process requirements.
Otherwise, it will affect the visual judgment of the color checker, especially double-bead, double-sided, rib, LYCRA rib, jacquard and other fabrics. Excessive door width difference will affect the color and light of the cloth surface.
Considering the factors of observer and fabric
In order to expand your ideas, we asked some people engaged in Printing and dyeing people consider other aspects such as color, light and fabric structure, and believe that:
1. Color: The reason why our eyes can see color is Because objects reflect light into the eye. If an object does not reflect light, we cannot see color, which is black. So which band of light enters our eyeballs?
We assume the color of the cloth based on the light reflected from the cloth surface. Different people have different reactions because their eyeballs are stimulated by light. Of course we do not It’s up to a color-blind or color-impaired colleague to decide whether the color of a piece of fabric is acceptable.
So where does the color of the fabric come from?
It is a mixture of the reflection of the yarn part and the light transmission of the gaps between the yarns. The same piece of fabric is viewed close up and viewed from a distance. , there is a certain difference in color, I believe everyone has this experience.
Instead of doing such an experiment, arrange yarns of the same color according to different densities and look at them at a certain distance on white paper. The colors will change. , as the density changes from small to large, the color gradually changes from light to dark.
2. The relationship between organizational structure and light reflection and light transmission: the flatter the surface of an object, the more light is reflected, and conversely, the more light is scattered. The surface condition of our fabrics is extremely complex. One is unevenness, the other is hairiness, and the third is the ratio of yarn density to void density.
The obvious example is that the color of the fabric surface will change after it undergoes a transparent coating, because its surface condition is changed by the action of the coating. Our fabric is drawn according to the contour after being magnified several times, which is a bit Similar to mountain peaks and valleys. If the peak is high, there will be no light at the bottom. If the peak is low, the reflected light and scattered light will change.
3. Shaping: Both the warp and weft directions (actually, we should say longitudinal and transverse directions) receive tension, so the surface condition of the fabric will definitely change. The result of this change is the light reflected into our eyeballs. Change, when it exceeds a certain limit, we feel that the color of the fabric has changed.
When the additive is used, it will change the color like a coating, such as forming a film on the surface of the fiber or yarn. Therefore, many finishing additives will specifically indicate that the use of this additive will not cause yellowing. Do not change the color, light, etc.
In order to more intuitively experience the impact of the environment on color, we can use the following picture to test, covering the middle line in the picture with your finger. Then experience the effects.
As long as the above measures are adopted during the production process and combined with reasonable pre-treatment and dyeing processes, I believe that a series of quality problems such as color flowers, color changes and decrease in fastness after finishing and shaping will be solved. It must be controlled within the range we require.
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