This article mainly outlines the process conditions of cold pad batch dyeing, the requirements for dyes, the requirements for alkali agents, the temperature and humidity requirements for dyed semi-finished products, the requirements for process distribution, controlling the guide fabric tension, and preventing the front and rear ends of the fabric. Color difference, constant speed, tension winding. Rapid prototyping of cold pad-batch dyeing and the energy-saving and consumption-reducing benefits of cold pad-batch dyeing.
Reactive dye cold pad-batch dyeing
In the past, reactive dye dyeing was based on moist heat treatment, such as high-temperature dip dyeing and continuous tie-dying. The main disadvantages were high energy consumption and easy generation of migration color difference. Fabrics that are sensitive to tension (such as cotton ammonia, cotton nylon, high-count and high-density down fabrics, etc.) and fabrics that are not easy to heat process (such as ramie, etc.) are prone to wrinkles during the processing process, affecting the feel of the fabric. From dyeing thermodynamics, we know that the dye loading is closely related to temperature. When the temperature is low, the dye loading that reaches equilibrium is high. But if the temperature is too low, the dye loading and fixation rates will also be low. Therefore, depending on the properties of different dyes and fibers Characteristics: Appropriately lowering the dyeing temperature and extending the dyeing time can not only improve the dyeing rate and color fixation rate, but also reduce energy consumption, salt consumption and pollution. Therefore, low-temperature dyeing in recent years, especially cold pad-batch dyeing, has become more Be taken seriously.
In the 1980s, when the world’s energy resources became increasingly tense, European countries successively researched and developed cold pad batch pre-treatment and cold pad batch dyeing technology. The cold pad batch dyeing process is between the dip dyeing process and the continuous pad dyeing process. It is a continuous process with the advantages of high efficiency, high quality, short process, energy saving and consumption reduction, and less pollution. The process is simple and reliable, with low basic costs and high production efficiency. The preparation time is short, the dye permeability and color fixation rate are high (15%-25% higher than the conventional two-phase pad steaming method), thereby reducing the amount of dye used in the process, the color of the sewage and the load of sewage treatment. Since there is no intermediate drying and steaming in the cold pad-batch process, it not only saves a lot of steam and electricity, but also does not cause the disadvantages of color difference caused by common dye migration caused by intermediate drying in the continuous pad-dyeing process.
The cold pad-batch dyeing process is popular in Europe and Southeast Asian countries. In recent years, more and more domestic dyeing and finishing companies have applied the cold pad-batch dyeing process to produce high-quality corduroy fabrics, Cotton-span elastic fabrics, anti-down high-density fabrics, cotton and linen blended fabrics and heavy khaki fabrics have achieved good economic benefits. However, the cold pad batch dyeing process also reflects some disadvantages.
In terms of improving head-to-tail color difference, package seam marks, dyeing reproducibility, improving color fixation rate, and excellent combination of suitable dyes and color-fixing alkali; improved As a proofing method, the efficiency of cold pad-batch dyeing is greatly improved, highlighting energy saving and consumption reduction. Therefore, it is increasingly used in the dyeing and finishing industry.
1. Cold pad batch process conditions
Requirements for dyes
The cold pad batch dyeing mechanism and the continuous pad dyeing mechanism are basically Similarly, it is also divided into three stages: adsorption, diffusion and fixation. Cold pad batch dyeing is to expand the fiber through the pad dyeing solution without heating, thereby transferring the dye to the interior of the fiber. Therefore, it requires good diffusibility of the dye and low fiber affinity and directness requirements to ensure the fabric’s quality. Equal dyeing should help overcome the slight color difference on the head. Because this process uses a large amount of alkali agents, in order to take into account the stability and reaction speed of the dye liquor, it is generally appropriate to use dyes with moderate reactivity. Vinyl sulfone reactive dyes have moderate reactivity. They are vinyl sulfate compounds that are soluble in water and do not show any activity in water. They are active only after adding an alkali agent and forming reactive vinyl sulfone through acid and alkali. The activated dye reacts with the hydroxyl groups on the cellulose to form ether bonds. In addition to having high resistance to acid hydrolysis, the ether bonds also play a major role in improving the color fixation rate.
During the dyeing process, the formation of vinyl sulfone is controlled so that the dye has sufficient time to diffuse into the fiber to obtain better level dyeing and through-dying effects, so vinyl sulfone Type dyes are particularly suitable for cold pad batch dyeing. The specifically applicable vinyl sulfone dyes include Remazol, domestic KN type, Japan’s Sumitomo Sumifix, Japan’s Mitsubishi Diamina, and Japan’s Mitsui Celmazol )dye. Others such as the monofluoro-s-triazine type include Cibacrom F (Cibacrom F), the difluoro-chloropyrimidine type including Clariant R/K (Drimarene), and the dichloro-s-triazine type. There are MX (Procion), domestic X-type dyes, monochloro-s-triazine-type K-type dyes, dual-reactive group domestic ME dyes composed of vinyl sulfone and monochloro-s-triazine type, etc.
① Among reactive dyes, vinyl sulfone dyes have an absolute advantage in price. The cost of red, maroon, brown, navy blue and black dyes in dyeing is 1/1 of other dyes. 3~1/5, this dye is the first choice for cold pad batch dyeing.
② Cold pad batch dyeing often requires several hours to more than twenty hours (depending on the type of dye) for color fixation reaction. Commonly used KN vinyl sulfone reactive dyes are prone to hydrolysis reactions when using caustic soda. When pH>8, under the condition of 30-35℃, the hydrolysis rate is 0.1% in 5 minutes, 1% in 10 minutes, and reaches 7.7% in 30 minutes. According to the measurement and explanation of reactive dye expert Vickstaff, the reaction speed of reactive dyes on fibers isThe dye reaction fixes the alkalinity. Although Na2Si03 also provides a certain degree of alkalinity, it mainly functions as a buffer, which can adjust the pH value of the alkali solution. It can not only improve the stability of the working solution, alleviate the hydrolysis of the dye, and improve the color fixation rate; it is also good for cloth The edge plays a protective role and can absorb CO2 in the air at the edge of the fabric, thereby maintaining the concentration of NaOH in it, making the edge of the fabric fully solid and preventing the phenomenon of deep, medium and shallow edges.
4. Pad dyeing solution
In order to slow down the hydrolysis of dyes in strong alkali and stabilize the dye liquor, after the padding working liquid is dissolved by the dye and alkali agent respectively, the dye liquor and alkali liquor are mixed in a ratio of 4:1 through a proportional pump and then injected into the padding tank. . The padding tank should be as small as possible, which can speed up the updating speed of the working fluid and reduce the residence time of the dye in the alkali agent. For velveteen products, the capacity of the dyeing tank of 30L is sufficient, but it must be equipped with a high-precision liquid level controller and a padding dyeing solution. A general uniform rolling car can be used, but it must be equipped with left, middle and right subdivision pressure gauges to strictly control the liquid rolling rate of the left, middle and right to reduce the color difference between the left, middle and right. The padding fluid temperature should be room temperature, which should not be lower than 20°C in winter and not exceed 30°C in summer. The liquid rolling rate is 85% ± 1%, and the vehicle speed is 24~26m/min. Excessive speed is detrimental to the fabric’s uniform liquid absorption and smooth winding. The chemical material should be treated with soft water, and after padding, it should be cleaned promptly with hot water dissolved in NaP03.
5. Rolling
When rolling, it is required to use a center-driven winding A-frame with constant linear speed and constant tension, so that the cloth surface can be wound smoothly and compliantly from beginning to end without any additional friction to ensure that the inner and outer layers of the cloth roll are evenly filled with liquid. When encountering seam joints, use plastic paper sheets about 20cm wide and 0.2mm thick at the top and bottom to eliminate seam head marks. After the entire roll of cloth is rolled, it should be tightly wrapped with plastic film to prevent moisture from evaporating and contacting the air to prevent wind marks. The volume of each roll of velvet cloth is generally about 100m long, regardless of the specification or variety.
6. Stacking
In order to prevent the dye solution from seeping out and depositing in the cloth roll, resulting in color difference between the upper and lower layers, the cloth rolls must be rotated evenly when stacked, and the rotation speed is generally 6 to 8 m/min. Because too low temperature will affect the diffusion of dye and the dyeing rate, therefore, When the room temperature drops below 20°C, insulation measures must be taken, and a cloth curtain can be used to surround the workshop for proper heating. When the room temperature is too high, it will also accelerate the hydrolysis rate of the dye on the cloth, which is not conducive to the fixation rate. Therefore, in high-temperature seasons above 35°C, high-temperature times during the day should be avoided, and stacking should be done at night and in the morning as much as possible. Theoretically, the stacking time should be more than 6 hours, but in order to ensure the uniformity of dyeing, it is generally stacked for 12 to 24 hours. Even if it is extended to 48 hours, it will not affect the color and depth of dyeing.
7. Washing
Washing The temperature is the order in which the clothes should be rolled on time. Those who roll them first should be washed first. According to the characteristics of velveteen, unwind it first and then wash it to ensure that it enters the machine smoothly. Washing can be carried out in an ordinary dry cleaning machine. Washing can be carried out according to the process of cold water washing → warm water washing (50°C) → warm water washing (70°C) → soaping 95°C (dispersant 8L, 5g/L) → warm water washing (80°C) → cold water washing. Before soaping, make sure the cloth surface is neutral and the pH value is below 8. If the fabric is dyed with deep colors and the fabric surface cannot reach neutrality, you can add HAc 1~2g/L for washing.
8. Examples
Color No.: 752 yuan color; production volume: 1184m; gray cloth specification: 9.7/18.2378/402112 weft weight velveteen.
Technical prescription: Remazine Black B133 6.98kg, Remazine Yellow 3BS 633g, Remazine Yellow 3RS 590g, Urea 120g, Penetrant JFC150g/120L, 38ºBe NaOH 7.95 kg, 40ºBe NaS03 9.75 kg/30L. The vehicle speed is 26m/min, the room temperature is 20-22°C, the stacking time is 20 hours, and the stacking temperature is heated to 22-24°C.
Process flow: padding→cold stack→cold running water→soap washing (dispersant 5 g/L) 95℃→hot water washing 95℃→cold running water washing→drying.
Cold pad-batch dyeing is the most suitable dyeing process for cotton velveteen products. Production practice has proven that using cold-pad-batch dyeing can improve the first-class rate of finished products and the dye fastness of fabrics.
Afterword
Leng Pad-batch dyeing significantly reduces production costs and achieves energy saving and emission reduction benefits. </p
