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How to prevent flashing in cotton/nylon dip dyeing?

Date:Dec 08, 2020

Flashing

On the surface, the flashing phenomenon is that the color hue dyed by cotton fiber and nylon fiber is inconsistent, that is, the hue is not flat. The fundamental reason is that some cotton dyes compete with nylon.

In actual production, the dyeing primary color and the second color matching can make full use of the competitive dyeing characteristics, so that the cotton fiber and nylon can be dyed with a purer color, the color is relatively flat, and the effect is good. But three color matching (such as army green, iron gray, brown) is difficult to dye to the same hue on two fibers at the same time, and the flashing phenomenon is serious. This is the most difficult problem encountered in the dyeing of cotton/nylon fabric. , Can be solved from the following three aspects.

1. Dyes

Generally, dyes for dyeing cotton (such as reactive dyes and direct dyes) have a certain degree of competition for nylon. Choosing new dyes that do not stain nylon can solve the problem of competition.


 2. Auxiliaries

In order to prevent the competitive dyeing of nylon, a special anti-dyeing agent for dyeing cotton/nylon mixed fabric can be used.


3. Process

Reactive dyeing is generally fixed at a pH of ll or more. Generally, the best dyeing pH of acid dyes for dyeing nylon is 5.5-6.0. That is, dyeing under acidic conditions. The two diametrically opposite process conditions make the reactive dyes dyed on the cotton fiber be stripped to varying degrees while dyeing nylon, which brings great difficulties to color imitation. Choose neutral dyes with milder dyeing conditions instead of acid dyes. The pH value of neutral dyes is about 6.5, which has little effect on reactive dyes, so that three color combinations such as army green, iron gray and brown can be dyed better. Same color effect.

Cotton 2


Color flower

Cotton/nylon mixed fabric is dyed in medium and dark colors, and dyed by reactive/acid two-bath method, generally dyeing cotton first and then nylon. According to the characteristics of the process, the stage of producing colored flowers can be divided into two stages: cotton colored flowers and brocade colored flowers.


1. Prevention and treatment of colored flowers in the cotton dyeing stage

1.1 Pre-processing

The pre-treatment of cotton/nylon mixed fabric is not thoroughly cooked, which is the main reason for dyeing cotton color. The pre-processing generally uses the following three methods:

a. Pre-treatment of jigger: large liquid volume, high rolling liquid temperature, low tension, not easy to produce wrinkles, and good scouring effect. However, it should be noted that except for the materials used, the temperature in the tank should not rise sharply to avoid wrinkles and defects in the nylon yarn. The temperature must be gradually increased from the first pass to the second pass to above 95°C; after constant, the number of treatment passes is more than eight passes, and after unwinding, it is fully washed on a flat washing machine to ensure the scouring effect.

b. Pre-treatment of cold reactor. The temperature is low, the reaction conditions are mild, and the treatment effect is not as good as that of the jigger. However, if the liquid volume is increased, the stacking time is extended, and the short steaming process is added, the scouring effect can be improved. The short-term steaming must be strictly controlled, and it is not suitable for track box steaming, otherwise stacking and crushing will occur.

c. Pre-treatment of overflow dyeing machine: This is a traditional treatment method with ideal results, but the process must be strictly controlled. The temperature must be gradually increased at a rate of 1°C/min; the valves before and after the overflow dyeing machine must be controlled properly, and the cloth speed must not be too fast, otherwise the cotton fibers on the cotton/nylon mixed fabric surface will rub against the inner wall of the dyeing tank and cause local dyeing. Uneven.


1.2 Dyes

Due to the different affinity of different dyes to the fiber, the difference in the dyeing rate of the dye to the fiber is caused. If the various process conditions are not properly controlled, it will produce color patterns and tank differences. Therefore, when formulating the dyeing process, the performance of the dye must be fully considered, and the dyes with good compatibility should be selected as much as possible, and the leveling agent should be added.


1.3 Operation during overflow dyeing

Due to improper operation, such as improper nozzle size, improper adjustment of the front and rear water flow valve switches, etc. The fabric will not flow smoothly in the cylinder, block the fabric, and cause uneven color flowers on the fabric. Therefore, the operator adjusts the mechanical equipment according to the tissue specifications of the fabric and formulates reasonable parameters to ensure that the fabric runs smoothly in the cylinder.


2. Prevention and treatment of colored flowers at the stage of dyeing

2.1 The cloth surface has uneven alkali

The uneven alkalinity on the cloth surface causes inconsistent dyeing of acid dyes on the cloth surface and the color is blurred. In response to this situation, before dyeing nylon in actual production, use 2~3g/L detergent to neutralize and wash once, so that the pH value of the cloth surface is uniform and weakly acidic, so as to avoid uneven alkali and cause stains. .

2.2 pH

The pH value has a great influence on the dyeing rate of acid dyes. When the pH value is less than 3, the nylon will be hydrolyzed and its strength will decrease. In actual production, if the pH value is controlled too high, when it is greater than 6, the dye uptake is slow, the time is long, and insufficient; when the pH value is less than 5, the dye uptakes quickly, and it is easy to produce uneven dyeing. Therefore, controlling the pH value between 5.5 and 6.0 can ensure uniform dyeing. Adding 0.5~1.5g/L dye stabilizer M-215 can reduce the fluctuation of pH value.

2.3 Temperature

The temperature of the dyeing bath is directly proportional to the dyeing rate of acid dyes. The higher the temperature, the faster the dyeing speed, especially when the temperature reaches 80℃ or higher, the dyeing rate will be faster, and it is easy to produce colored flowers. In view of the temperature characteristics, a heat preservation stage is added during mass production, the light color is 50~60℃, and the heat preservation is 15~20min. The heating rate is preferably 1°C/min.

2.4 Chelating dispersant

If the water quality is good, chelating dispersant can be added, and 0.5~1.5g/L chelating dispersant M-175 can be added to the poor water quality.

2.5 Levelling agent

When dyeing, add level dyeing .0 5~2g/L. Nylon leveling agent is zwitterionic and amphiphilic leveling agent. It can not only be combined with nylon to eliminate the difference in nylon fiber affinity, it has good nylon dyeing horizontal strip coverage, but also can be combined with dye relaxation, has a good retardation and migration effect, and will not affect the final color yield. For color strip fabrics, the pre-scouring process can be used, and the dyeing and serious color difference fabrics can be repaired by migration dyeing.