Dyeing Basics: Dyeing of Acrylic Fibers

1. Dyeing water

Since the cationic dyes are dyed with strong acid groups, acrylic fibers are easily affected by metal ions such as calcium ions in water. Furthermore, some cationic dyes are also susceptible to metal ions. If the water quality is not suitable for dyeing, it must be treated accordingly to reduce the adverse effects of water on dyeing.

In addition, if the tap water contains active chlorine, it must be deactivated before it can be used.

2. Refining

Simple scouring is carried out on demand to remove the spinning oil on the acrylic fiber, the slurry on the previous process and various contaminations, so that the subsequent processes such as dyeing and finishing can be carried out smoothly.

The following simple scouring treatment can be performed on acrylic fibers:

Nonionic surfactant 0.5～1.0g/L

Processing temperature 60℃

Processing time 20～40min.

There are many varieties of scouring aids used for scouring, which can be selected from many products produced by many manufacturers.

3. Bleaching and whitening

The whiteness of acrylic fibers is already quite high. If higher whiteness is also required, fluorescent whitening treatment is required or combined with chemical bleaching.

The use of fluorescent whitening agents for whitening treatment is simple and widely used. There are two types of fluorescent whitening agents: cationic fluorescent whitening agents and dispersion fluorescent whitening agents. According to the dyeing method of cationic dyes or disperse dyes, whitening treatment is carried out respectively. Due to the better levelness when using a dispersion type fluorescent whitening agent, a dispersion type fluorescent whitening agent is often used. There are also many manufacturers of fluorescent whitening agents for users to choose from.

Fourth, the formulation method of cationic dye dyeing process

1. Determine the dyeing formula

The dyeing formula is determined according to the practical properties such as the dyeing fastness of the final product, the type of dyeing machine, etc. In general, formulations can be determined in the following order.

a) Properly mix the dyes according to the sample and make a small sample. By repeating the color matching, until the color that matches the sample is obtained;

b) After the prepared color is consistent with the incoming sample, decide the amount of dye to be used. At the same time, the retarder is selected, and the optimal dosage of the retarder is calculated according to the DC value calculation method described in the first chapter;

c) Set the dyeing temperature program. For the above a) and b), it is best to carry out a dip dyeing experiment to confirm whether the levelness meets the requirements;

d) Use a small dyeing machine to confirm whether the dyeing fastness meets the requirements;

e) If the dyeing uniformity and dyeing fastness do not meet the requirements, continue the test until the required formulation is obtained.

2. The role of several additives

In addition to retarders, the surfactants that play a leveling role in the dyeing process also have a class of leveling agents that play a role in migration, such as the domestic leveling agent XFM-2. This type of leveling agent is a low molecular weight cationic quaternary ammonium compound, which has a good migration effect and can be used for the dyeing of M-type cationic dyes and the dyeing and repairing of dyes with K=5. Because of its low molecular weight, it generally does not occupy the dye base and has no effect on Sf.

Acetic acid is the main dyeing auxiliaries for cationic dyes to dye acrylic fibers. It provides hydrogen ions in the dye bath to help dye dye. In most cases, a buffer solution is formed with sodium acetate to stabilize the pH of the dye bath. Acetic acid also has the function of dissolving cationic dyes. When dissolving the material, use acetic acid to adjust the size and wash it with boiling water.

In many cases, urea is also added to aid solubility. This is because the acyl diamino group in the urea molecular structure can relieve the interaction force between the cationic dye molecules and the bond energy of the hydrogen bond, so that the dye associates rapidly dissociate into a single molecule state. The sufficient dissolution of the dye is beneficial to prevent the appearance of stains. Urea has an amino group in its structure, and its cation content is 2.5 times that of sodium, so it has a better leveling effect than ammonium sulfate.

Ammonium sulfate is an acid release agent. With the increase of dyeing temperature, ammonia gas is gradually precipitated, acid is left in the dye bath, the pH value is reduced, and the dyeing speed is also decreased, which is conducive to obtaining level dyeing. For dyes with excessive dyeing concentrated in high temperature areas, an appropriate amount of ammonium sulfate can be added to ease the dyeing.

3. Control of dyeing temperature

For acrylic fibers, the movement of polymer segments is only possible above the glass transition temperature. The space created by this segment movement makes it possible for the dye molecules to penetrate, diffuse and fix inside the fiber to complete the dyeing.

The chain segment movement of polymers is greatly affected by temperature. Above the glass transition temperature, the degree of chain segment movement increases significantly for every 1 °C increase. This explains why above the glass transition temperature, the dyeing speed increases sharply with the increase of temperature, even to the extent that the dyeing speed increases by 30% for every 1 °C increase. For acrylic fiber, it is precisely because of the violent chain segment movement of its polymer and the strong Coulomb force between the acidic group in the molecule and the cationic group in the dye component, which causes a large number of concentrated dyeing in a narrow temperature range. The phenomenon.

The control of the dyeing temperature is to make the dye evenly dyed within this narrow temperature range, and strictly let the temperature rise and fall according to the requirements of the process, and the error is as small as possible.

4. Several dyeing methods of acrylic fiber

In general, a reasonable dyeing process can be formulated. Common dyeing methods include constant temperature rapid dyeing, saturation dyeing and ordinary dyeing.

The constant temperature rapid dyeing method refers to dyeing at a temperature above the glass transition temperature and below the boiling point, and keeping the temperature for 45 to 90 minutes. , and then slowly cool down to 50 ℃, rinse out the method of the car. The key to this method is to choose a constant temperature for dyeing. Due to the emergence of the third-generation retarder, the insurance factor of this method has been greatly improved. In addition, the dyeing formula of this method is also relatively simple. The general composition includes buffer solution composed of acetic acid and sodium acetate, dye retarder A below 0.2% and levelling agent 1227 of 0.3% to 0.5%. When the amount of dye is large, 2.0 to 3.0% of urea is added. Install the dyed object, add water to raise the temperature to 5°C below the set temperature, add all auxiliaries (except chemical auxiliaries), run for 10-15min. Then add fully dissolved dye liquor, and run to the set temperature properly, Keep warm.

The saturation dyeing method refers to the dyeing method in which the sum of the products of the dyes and retarders in the composition of the dyeing formula and the respective f value is equivalent to the dyeing saturation value of the acrylic fiber.

The key to the saturated dyeing method lies in the control of the dosage of the second-generation retarder.

The common dyeing method is a dyeing method that combines the advantages of the dyeing method that does not add retarder to control the temperature and the dyeing method that the retarder controls the temperature at the same time, and uses the characteristics of the third-generation retarder. Leveling agent 1227 and retarder A in the dyeing formula work synergistically. Leveling agent 1227 plays more role in diffusion penetration and cleaning. The dosage of retarder in the formula is 0.02%-0.4%, and the dosage of leveling agent 1227 is 0.2%-0.5%.

In addition, with the development of dyes suitable for acrylic fibers, migration-type cationic dye dyeing methods and disperse-type cationic dye dyeing methods have also been developed in recent years. No introduction is made here.

5. Correction of color and stain

In the dyeing process using cationic dyes, if it is found that it is inconsistent with the incoming sample, please deal with it according to the following methods. That is, before adding the cationic dye liquor, the temperature of the dye bath should be lowered to 80°C. After adding the dye liquor, the liquid temperature should be kept at 80°C, stirred for 5 minutes, and then heated up to the boiling point again after stirring to correct the color. Before that, it's best to make a sample first.

When stained spots appear, treat as described in Chapter 1.

When dyeing with cationic dyes, if the uneven dyeing is quite serious, decolorization treatment is required. At this point, chlorine bleaching is required to chemically decompose the dye, and then re-dye.

Despite the above-mentioned corrective measures, this will also reduce the quality of dyeing, and even lose the reputation of the dyeing factory. Therefore, before the actual dyeing, we must carefully make samples, conduct level dyeing and color matching experiments, and prevent accidents from happening, thereby minimizing losses.

6. Other matters needing attention

In order to dye a dark color, corresponding measures can be taken in actual production, so that the functional groups on the fiber can fully react with the dye to obtain a dark color. Specific measures include:

1) Increase the PH value of the dye bath, so that the acid functional groups of the fiber can be fully ionized and combined with the dye;

2) Add a small amount of carrier, such as β-naphthol, etc.;

3) Reduce the dosage of the second generation cationic retarder;

4) Extend the time of boiling dyeing, or use high temperature dyeing above 100℃.

The level dyeing of acrylic fiber is mainly achieved by controlling the dyeing speed. Different brands of acrylic fibers have different dyeing rates. Therefore, before dyeing, it is necessary to understand the properties of the acrylic fiber to be dyed. Then choose the appropriate dye to solve this problem.

In addition, the key dyeing temperature range in the dyeing formula can be found through the dyeing rate curve, and level dyeing can be obtained by keeping warm in this temperature range or delaying the heating rate.

5. Special attention

Finally, regardless of the dye, method, or machine used, some operational issues are common and require special attention:

1) Chemicals: some additives, such as acetic acid, need to be added to the beating;

2) Cooling down: Because the dyeing of acrylic fiber is above its glass transition temperature. If the temperature is suddenly lowered, the degree of hardening of the fibers will be different due to the inconsistent degree of cooling, which will seriously affect the feel. Therefore, it is necessary to cool down slowly;

3) Softening treatment: cationic additives are commonly used in the softening treatment of acrylic fibers.