First, dyeing water
Since the position where the cationic dye is dyed is a strong acidic group, the acrylic fiber is easily affected by metal ions such as calcium ions in the water. Moreover, some cationic dyes are also susceptible to metal ions. If the water quality is not suitable for dyeing, it must be treated first to reduce the adverse effects of water on the dyeing.
In addition, if the tap water contains active chlorine, it must be removed before it can be applied.
Simple refining is carried out as needed 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 proceed smoothly.
The following simple scouring treatment can be applied to the acrylic fiber:
Nonionic surfactant 0.5～1.0g/L
Processing temperature 60 ° C
Processing time 20 ~ 40min.
There are many types of scouring aids for scouring, which can be screened from many products produced by many manufacturers.
Third, bleaching and whitening
The whiteness of acrylic fibers is already quite high. If higher whiteness is also required, fluorescent whitening or a combination with chemical bleaching is required.
The use of a fluorescent whitening agent for whitening treatment is simple and widely used. Fluorescent whitening agents include cationic fluorescent whitening agents and dispersive fluorescent whitening agents. According to the dyeing method of cationic dye or disperse dye, whitening treatment is separately carried out. Since the leveling property when using a dispersion type fluorescent whitening agent is good, a dispersion type fluorescent whitening agent is often used. There are also many manufacturers of fluorescent whitening agents available for users to choose from.
Fourth, the formulation method of cationic dyeing process
1, decide the dyeing formula
The dyeing formula is determined according to practical properties such as the color fastness of the final product, the type of dyeing machine, and the like. Generally, the formulation can be determined in the following order.
a) Properly mix the dye according to the sample and make a small sample. By repeating the color matching until a color that matches the sample is obtained;
b) After the blended color is consistent with the sample, determine the amount of dye used. Simultaneously select the retarding agent and calculate the optimum amount of retarding agent according to the DC value calculation method described in Chapter 1;
c) setting the dyeing temperature program. For the above a) and b), it is best to carry out the dip dyeing test first to confirm whether the leveling property meets the requirements;
d) confirm whether the color fastness meets the requirements by a small dyeing machine;
e) If dyeing uniformity and dye fastness are not met, continue the test until the desired formula is obtained.
2, the role of several additives
In addition to the retarding agent, the surfactant which is leveled in the dyeing process has a leveling agent which acts as a transfer dye, such as the domestic leveling agent XFM-2. These leveling agents are low molecular weight cationic quaternary ammonium compounds with good transfer dyeing effect, which can be used for the dyeing of M-type cationic dyes and the dyeing and color correction of K=5 dyes. Because of its low molecular weight, it generally does not occupy the dyeing seat and has no effect on Sf.
Acetic acid is the main dyeing agent for the dyeing of acrylic fibers by cationic dyes. It provides hydrogen ions in the dye bath to help dye the 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, and the chemicals are adjusted with acetic acid and pulverized with boiling water.
In many cases, urea is also added for solubilization. This is because the acyl diamino group in the molecular structure of urea can release the interaction force between the cationic dye molecules and the bond energy of the hydrogen bond, and the association of the dye is rapidly dissociated into a single molecule state. The full dissolution of the dye helps to prevent the appearance of stains. Since urea has an amino group in the structure and the amount of cation is 2.5 times that of sodium, it has a better leveling effect than ammonium sulfate.
Ammonium sulphate is an acid release agent. As the dyeing temperature increases, ammonia gas is gradually precipitated, and acid is left in the dyeing bath to lower the pH value, which also leads to a decrease in dyeing speed, which is favorable for obtaining leveling. For dyes that have been dyed in a high temperature region, ammonium sulfate may be added in an appropriate amount to alleviate the dyeing.
3. Control of dyeing temperature
For acrylic fibers, the segmental motion of the polymer is only above the glass transition temperature. The space created by the movement of the segment makes it possible for the dye molecules to penetrate, diffuse and fix inside the fiber, thereby completing the dyeing.
The segmental motion of the polymer is greatly affected by the temperature. Above the glass transition temperature, the degree of segmental motion increases significantly for every 1 °C increase. This explains why the dyeing speed rises sharply with increasing temperature above the glass transition temperature, and even increases the dyeing speed by 30% for every 1 °C increase. For acrylic fibers, it is due to the intense chain motion of the polymer and the strong Coulomb force between the intramolecular acidic groups and the cationic groups in the dye group, resulting in a large concentration of dyeing in a narrow temperature range. The phenomenon.
The control of the dyeing temperature is to uniformly dye the dye in this narrow temperature range, and strictly raise the temperature according to the requirements of the process, and the error is as small as possible.
4. Several dyeing methods for acrylic fiber
In general, a reasonable dyeing process can be developed. Common dyeing methods include constant temperature rapid dyeing, saturated staining, and common staining.
Constant temperature rapid dyeing method refers to dyeing at a temperature above the glass transition temperature and below the boiling point, and keeping it for 45-90 minutes. After most of the dye is exhausted, it is heated to the boiling point fixing color, and the fixing time is short. Then slowly cool down to 50 ° C and rinse out the car. The key to this method is to choose a temperature that is thermostated. Due to the emergence of the third generation of retarding agents, 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 is a buffer solution composed of acetic acid and sodium acetate, a retarder A of 0.2% or less, and a leveling agent 1227 of 0.3% to 0.5%. When the amount of the dye is large, 2.0 to 3.0% of urea is added. Install the dyed object, add water to the temperature below 5 °C, add all the additives (except additives for the chemical), run for 10 to 15 minutes. Then add the fully dissolved dye solution and operate to the set temperature. Keep warm.
The saturated dyeing method refers to a dyeing method in which the sum of the amount of the dye and the retarding agent in the composition of the dyeing composition and the respective f-values is equivalent to the dyeing saturation value of the acrylic fiber.
The key to the saturated dyeing method is the mastery of the amount of the second-generation retarder. The amount of the dye has a direct influence on the shade of the color and the shade of the hue.
The common dyeing method is a combination of the dyeing method that does not add a retarder to control the temperature and the dyeing method that simultaneously controls the temperature rise, and the characteristics of the third generation retarder, and a dyeing method with a wide adaptability. Levelling agent 1227 and retarder A in the dyeing formulation act synergistically. Levelling agent 1227 acts more as a diffusion penetration and cleaning. The dosage of the retarding agent in the formulation is 0.02% to 0.4%, and the amount of the leveling agent 1227 is 0.2% to 0.5%.
Further, in recent years, with the development of dyes suitable for acrylic fibers, migration type cationic dye dyeing methods and dispersion type cationic dye dyeing methods have been developed in recent years. I will not introduce it here.
5, color and stain correction
In the dyeing process using cationic dyes, if it is found to be inconsistent with the sample, please proceed as follows. That is, before the cationic dyeing solution is added, the temperature of the dyeing bath is lowered to 80 ° C, and the liquid temperature of 80 ° C is also maintained after the dyeing solution is added, and the mixture is stirred for 5 minutes. After stirring uniformly, the temperature is raised again to the boiling point, and the color can be corrected. Before that, it is best to play a sample first.
In the case of staining, it is treated as described in Chapter 1.
When dyeing with a cationic dye, if the uneven dyeing is quite severe, a decolorization treatment is required. At this point, chlorine bleaching is required to chemically decompose the dye and then re-stain.
Despite the above-mentioned corrective measures, this will also reduce the dyeing quality and even lose the reputation of the dyeing factory. Therefore, before the actual dyeing, it is necessary to carefully carry out the sample, perform the leveling and color matching experiments to prevent the occurrence of accidents, thereby minimizing the loss.
6, other matters needing attention
In order to be able to dye dark colors, corresponding measures can be taken in actual production so that the functional groups on the fibers can fully react with the dye to obtain a dark color. Specific measures are:
1) increasing the pH of the dye bath so that the acidic functional groups of the fiber can be fully ionized to bind to the dye;
2) adding a small amount of a carrier such as β-naphthol or the like;
3) reduce the amount of second-generation cationic retarder;
4) Extend the time of boiling, or use high temperature dyeing above 100 °C.
The leveling of acrylic fiber is mainly achieved by controlling the dyeing speed. Acrylic fibers of different brands have different dyeing rates. Therefore, it is necessary to understand the properties of the acrylic fiber to be dyed before dyeing. Then choose the appropriate dye to solve this problem.
In addition, the dyeing rate curve can be used to find the key dyeing temperature interval in the dyeing formula, and the leveling can be obtained by keeping the temperature in this temperature range or delaying the heating rate.
Five, pay special attention
Finally, no matter what kind of dye, method, or machine, some operational problems are common and require special attention:
1) Chemical: It is necessary to add some additives such as acetic acid in the beating;
2) Cooling: Because the dyeing of acrylic fibers is above its glass transition temperature. If the temperature is suddenly lowered, the degree of hardening of the fiber will be different due to the inconsistent cooling degree, which seriously affects the hand feeling. Therefore, it is necessary to slowly cool down;
3) Soft treatment: The soft treatment of acrylic fiber is commonly used as a cationic auxiliary.