Nylon is the trade name of synthetic polyamide fiber, commonly known as nylon, the basic composition of the material is through the amide bond -NHC0 connected aliphatic polyamide, often used in textile fabric nylon nylon 6 and 66. Polyamide macromolecule is mainly composed of three parts, namely the hydrophobic methylene part, the hydrophilic amide group and the amino and carboxyl groups of the chain end. Although the amino content of polyamide is low, but its molecular chain has a large number of methylene groups that can form van der Waals force and hydrogen bond with dyes, so polyamide can be combined with anionic dyes by ion bond form, but also through strong van der Waals force and dye interaction and coloring. Although there are some small differences in molecular structure and dyeing properties between polyamide 6 and polyamide 66, the dyeing and finishing process of polyamide 6 is the same.

Nylon fiber because of its good strength, good wear resistance, moisture absorption than polyester fiber, comfort than polyester clothing is good, has been widely used in clothing fabrics, high-grade underwear, sports clothing and mountaineering clothing. Due to the development of the market and the progress of the spinning technology, most of the nylon fabric has increased the elastic fiber (spandex) to enhance the wear resistance and resilience of the nylon fabric, which increases the difficulty of the dyeing and finishing of the nylon fabric.

01

Horizontal stripes

Cause analysis:

Polyamide fibers on fabrics differ in chemical or physical characteristics:

(1) Physical differences of yarns, including the number of yarns, the root number of fibers in the yarn or the fiber size, and the difference between the end crimp of a single fiber or the end crimp of multiple fibers in the yarn.

(2) The chemical difference originates from the different amino content of the fiber, which may be caused by the spinneret process, the hot drafting process, or the filamentous process. For example, the inhomogeneity of supramolecular structure produced by nylon fiber in the process of treatment, such as the difference of crystallinity and orientation in the fiber or the inhomogeneity of the cored structure.

The solution:

(1) Strengthen the detection of grey cloth, and choose light color, original white or added white if there are differences.

(2) Choose dyes with good coverage and evenness. Dispersive dyes have better coverage and evenness than acid dyes, so some dispersive dyes can be added.

Color flower caused by 02 dyeing

Cause analysis:

The content of terminal amino group in polyamide is less and the saturation value is low. When two or more dyes are dyed together, competition for dyeing position will occur, which is called race dyeing phenomenon. If the dye selected in the dyeing rate and affinity of the difference is large, in different dyeing time, the fiber dyed color will be very different, resulting in large and small sample color difference and poor reproducibility.

The solution:

Select the dyeing material series suitable for the production machine with similar dyeing curve and affinity, good compatibility. When MASTERING THE dyeing properties OF various DYES AND selecting dyeing materials, THE dyeing rate, dyeing curve, evenness, color fastness, and sensitivity to temperature and evenness SHOULD be considered comprehensively.

(1) Give full consideration to the compatibility of dyes

When several dyes are used in combination dyeing, the appropriate dye should be selected and the amount of dye should be controlled. Generally, we should try to choose the same series of dyes from the same company. Even if we have to choose dyes from different companies, we should try to choose dyes with similar dyeing curve, similar initial dyeing temperature, and similar sensitivity to temperature and leveling agent, so as to avoid competing dyeing.

(2) Pay attention to the difference in dyeing of large and small dye samples

Some dyes are not obvious when they are dyed in small samples, but they are completely exposed in large-scale production. For example, in the production of lake green and peacock blue, a similar problem occurs when acid turquoise blue and acid yellow are used together. This is due to the large molecular structure of acid turquoise blue, and acid yellow dyeing curve is very different, so it causes competitive dyeing. If the use of acid blue and acid green with yellow light together, basically solved the problem of dyeing.

03 Process conditions caused by the color flower, etc

The dyeing process of polyamide is very demanding. The process condition is an important factor affecting the color and evenness of the dyed products, such as temperature and pH value will affect the quality of the products.

Improper process is easy to produce defects such as poor evenness, color, color, fastness and so on.

1. Control the initial dyeing temperature and heating rate

Nylon is a kind of thermoplastic fiber, so the dyeing rate of the fiber is closely related to the temperature, the dyeing temperature must be higher than the glass temperature of the fiber (35 ~ 50℃). Nylon fiber began to adsorb dye at 40℃, and the dyeing rate accelerated with the increase of temperature, and the dyeing process could be basically completed at 100℃. Although the dyeing can be basically completed when the temperature is 100℃, the further heating will help the dye to migrate and thus improve the evenness. However, if the heating rate is not well controlled, it is easy to produce uneven dyeing phenomenon.

The effect of temperature on dye dyeing rate is also different with different dyes. The dyeing rate of uniform dyes increases gradually with the increase of temperature. The dyeing rate of shrinkable dye starts to increase rapidly with the increase of temperature after the dyeing bath temperature is higher than 60℃. Especially in the temperature range of 65 ~ 85℃, the control of the heating rate is the key to the success or failure of nylon dyeing. If the control is not proper, it will cause the problems of fast coloring, poor dyeing, easy to spend and difficult to repair. If shrinkable dye is used to dye nylon, the initial dyeing temperature should be room temperature, at 65 ~ 85℃ temperature section, strictly control the heating rate of 1℃/min, and add the dyeing agent, take step heating method; Then the temperature was raised to 95 ~ 98℃ and the temperature was held for 45 ~ 60min.

In addition, the dyeing properties of the fiber also changed with the heat treatment conditions before dyeing, and the dyeing rate of the fiber after dry heat solidification decreased significantly.

2, control the pH value

When dyeing polyamide fiber, when the pH value of dyeing solution is relatively high, the dye is rarely dyed; When the pH value of the dye solution fell to a certain value, the dye began to dye, and soon reached saturation. The pH value continued to decrease during the dyeing night, and the dye did not increase significantly. However, when the pH value further decreased to 3, the amount of dye dyeing increased sharply, and super-equivalent adsorption occurred.

When nylon fiber is dyed at a very low pH value, it will be hydrolyzed, especially after super-equivalent adsorption, the pH value in the fiber is lower than that in the solution, and the hydrolysis is accelerated. After hydrolysis, more amino groups are produced, and the accessibility of the fiber is increased, and more dyes can be adsorbated, so it is easier to produce uneven dyeing phenomenon. Therefore, according to the actual situation, appropriately adjust the pH value to reduce the phenomenon of color flower.

Weak acid dye dyeing nylon, the pH value of light color is generally controlled in 6 ~ 7(can be adjusted by dyeing stabilizer M-21 5), and improve the dosage of leveling agent, in order to strengthen leveling, avoid dyeing flowers, but the pH value can not be too high, otherwise the color will fade; The pH value of dyeing dark color is 4-6 (can be adjusted by dyeing stabilizer M-215), and the appropriate amount of acetic acid is added in the process of holding heat to reduce the pH value and promote dye dyeing.

3. Pay attention to the selection and dosage of leveling agent

According to the characteristics of poor evenness and coverability of nylon dyeing, it can be used with dye in the same bath, and can also be used to treat nylon before dyeing with evenness. Anionic HOMOGENIZER IS DISSOCIATED INTO NEGATIVE IONS IN DYEING BATH AND ENTERS THE fiber, WHICH OCCUPIES THE LIMITED DYEING BASE ON NYLON FIBER AT FIRST, AND THEN IS REPLACED BY DYE gradually WITH the increase OF temperature IN THE dyeing process, which REDUCES THE binding speed BETWEEN dye and fiber and ACHIEVES the purpose OF HOMOGENization. The non-ionic homogenizer is hydrogen bonded to the dye in the dyeing bath, and then the dye is gradually decomposed and released in the dyeing process, and adsorbed by the fiber.

The addition of leveling agent can significantly improve the evenness and capping dyeing ability, but with the increase of the concentration of additives, the dyeing rate decreases, leading to different degrees of decline in the exhaustion rate, so the amount of leveling agent should not be too much. Because in the process of dyeing, the leveling agent not only plays a leveling effect, but also has a blocking effect. If the amount of homogenizer is too large, the dyeing rate of acid dye will be reduced, the concentration of dyeing residue will be increased, and the color difference of large and small samples and the poor repeatability will be caused. Generally, when dyeing light color, the amount of leveling agent is larger; When dyeing dark color, the amount of leveling agent is less.

04 yellowing

In the process of storage and transportation, the appearance and quality of nylon light-colored fabric are affected by slight local yellowing phenomenon.

Cause analysis:

1, plastic bags with pollutants and BHT(butylated hydroxyl anisole) and nylon chemical reaction, resulting in color variation, resulting in yellowing.

2, the selection of anti-phenol yellowing agent dip-dyeing or dip-rolling treatment

conclusion

To sum up, the dyeing effect of polyamide fiber is affected by many factors. Therefore, according to the specific dyeing requirements, appropriate dyes, additives, predetermined process and dyeing conditions such as pH value, temperature and time of Zuijia should be selected in practical operation. Only by combining these factors can a good dyeing effect be obtained.