In production, it is often encountered that polyester or polyester-containing fabrics have normal color and light after being dyed out of the vat, but then the color and light do not match after finishing in the next process, resulting in discoloration or local spots, streaks, and color fastness. Such problems may be minor and can be repaired through re-repair, but severe problems may not meet the requirements even after re-repair, which will have a certain impact and loss on the factory’s normal production, delivery, quality and efficiency.
The following is a brief explanation of its causes and preventive measures for reference.
Reasons for poor color fastness of polyester fabrics after shaping
For customers with high requirements for polyester color fastness, the dyeing factory undergoes high temperature during the actual production process. After high-pressure dyeing, reduction cleaning, and high-temperature setting, the ideal color fastness is still not achieved.
The reason is: Thermal migration of polyester after dyeing with disperse dyes is the key to the above problems. Thermal migration is a common property of disperse dyes. 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 tubes 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 the thermal migration of disperse dyes with different structures are also different, and the differences between them are also large, so after finishing, high-temperature setting Especially when using silicone oil and antistatic, it contains a certain amount of surfactants. When these additives are unevenly adsorbed on the cloth surface, including uneven PH on the cloth surface, the above-mentioned so-called color flowers and colors will be produced. A series of problems such as deformation and decrease in fastness such as friction, washing, staining, etc. This phenomenon often manifests itself as one or more coexistences, which brings insurmountable hidden dangers and hazards to the dyeing quality.
Treatment measures
1. First, choose disperse dyes with small and similar thermal migration. Because the molecular weight of these dye structures is larger, the affinity with polyester fiber is also larger, so It is difficult to migrate from the interior of the fiber to the surface.
2. When selecting color matching dyes, try to use the same type or high-temperature dyes. 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 dyes is not consistent with the sublimation fastness, high-temperature dyes have less sublimation of dyes under higher temperature setting, and the stability of the corresponding color light is also better.
3. Post-finishing uses a gentler process. The darker the color, the more the dye will migrate. The higher the temperature, the greater the impact on migration. It depends on the variety while ensuring the styling effect. Temperatures of 150°C or lower can be used to avoid or reduce dye migration.
4. When choosing a finishing softener, try to use hydrophilic silicone oil or self-emulsifying block silicone oil that does not contain emulsifiers. This type of silicone oil has good stability and low discoloration and yellowing. It has a better preventive effect on dye migration.
5. 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 the alkaline insurance powder process is used, It must be neutralized, because some dyes are 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 cannot even be repaired.
Factors affecting color changes during styling
The design of the shaping process is based on the status of the B/F fabric: door width, It is set according to weight, strength and shrinkage. Among them, the following parameters have a greater impact on color changes.
1. Temperature over resin: dark color: 170℃; light color (sensitive color): 150℃, but resin: 150℃. Dry cloth: 130-160℃. The temperature is 100 when the cloth is dry. -150℃ has little effect on color. When it is greater than 150℃, the higher the temperature, the greater the effect on color.
2. The speed is 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 is less than 200GM) If the cloth surface does not dry during actual operation, first check whether the machine is normal; if so, first notify the person in charge of the process to slow down the machine speed and make changes to the process. Under the same temperature, keeping the cloth surface dry (0-6% moisture content) with a difference of 2-3M/MIN will have negligible impact on the cloth surface.
3. Circulating air a>. Generally, Class II air is used to pass through the resin. The thermal efficiency is higher than Class I, and the impact on the color is greater than Class I; b>. However, the resin is denser and the thicker structure requires Use Class II wind; loose and unstable fabrics can use Class I wind. The final shape is subject to dryness of the cloth, and the impact on the color is negligible at the same temperature.
4. Materials a>. The resin and catalyst react chemically with the fiber and combine covalently, changing the molecular arrangement inside the fiber, which has a greater impact on the color change of the fabric; b>. The amount of resin and catalyst The larger the value, the greater the impact on color, otherwise the impact will be reduced; c>. The impact 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 surface than soft oil with a clean and white appearance. Cationic soft oil (surfactant) has a greater impact on the color of the cloth surface than non-ionic soft oil. In short, in a final recipe combination�The higher the amount of resin and soft oil added, 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 a priority to consider when designing the process.
5. When designing the door width 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 fabric warp and weft directions The shrinkage is relatively average (such as 6×6%, 7×7%). The post-finishing and trial-fitting personnel should check the post-finishing and shaping process before doing trial trimming to ensure that the door width meets the process requirements. Otherwise, it will affect the visual judgment of the color checker, especially for 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
To expand everyone’s ideas, we asked some people who are engaged in printing and dyeing to consider the reflection of color, shade and fabric structure. Considering other aspects, I think:
1. Color: The reason why our eyes can see colors is because objects reflect light and enter the eyes. 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 will not let a color-blind or color-weak colleague make the decision. 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 will have a certain color difference when viewed close up and viewed from a distance. I believe it Everyone has this experience.
Let’s do this experiment. Arrange yarns of the same color according to different densities and look at them at a certain distance on white paper. The color changes. As the density changes from small to large, the color changes from light to light. Gradient to darker.
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 clear coating, because its surface condition is changed by the action of the coating. Our fabric is enlarged several times and drawn according to the outline, somewhat similar to peaks and valleys. If the peak is high, the valley bottom will be dark; if the peak is low, the valley bottom will be bare. Reflected light and scattered light change as it changes.
3. Shaping: Both the warp and weft directions (actually, we should say longitudinal and transverse directions) are under tension, so the surface condition of the fabric will definitely change, and the result of this change is reflected into our eyeballs When the light changes beyond a certain limit, we feel the color of the fabric changes.
The use of additives will sometimes change the color like a coating, such as film formation on the surface of fibers or yarns. Therefore, many finishing additives will specifically indicate that the use of this additive is not required. Yellowing, no change in color and light.
In order to more intuitively experience the impact of the environment on color, we can use the following picture to test, cover the middle line in the picture with your finger, and then experience the effect.
Notes
As long as the above measures are adopted during the production process and combined with reasonable pre-treatment and dyeing processes, I believe that the final finishing can be achieved After a series of quality problems such as color bloom, discoloration and fastness decrease, they will be able to be controlled within the scope of our requirements.
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