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.
Cold pad-batch dyeing with reactive dyes
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. However, if the temperature is too low, due to the dye loading rate and color fixation, The dyeing rate will also be low. Therefore, according to the characteristics of different dyes and fibers, appropriately lowering the dyeing temperature and extending the dyeing time can not only increase the dyeing rate and color fixation rate, but also reduce energy consumption, salt consumption and pollution, so In recent years, low-temperature dyeing, especially cold pad-batch dyeing, has received more attention.
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.
Second cold rolling batch process conditions
1. Requirements for dyes
Cold pad The dyeing mechanism is basically the same as that of continuous pad dyeing, and 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 It has better leveling and through-dying effects, so vinyl sulfone 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 h Neimen Procion 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. In dyeing, red, maroon, brown, The cost of navy blue and black dyes is 1/3 to 1/5 of other dyes, and these dyes are the first choice for cold pad-batch dyeing.
② Cold pad batch dyeing often requires several hours to more than 20 hours (depending on the type of dye). 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 exceeds the reaction rate with water, and the increase in pH has little impact on the reaction rate.e/2021/07/15/20210715094239157014.png”>
Urea has the function of helping to dissolve and expand fibers, and NaOH provides sufficient dye reaction Fixed alkalinity. Although Na2Si03 also provides a certain amount of alkalinity, it mainly acts as a buffer and 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 efficiency; it also protects the edge of the fabric 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 dark, 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 fluid is dissolved by the dye and alkali agent respectively, the dye liquor and alkali liquor are adjusted to a ratio of 4:1 through a proportional pump. After mixing, pour into the rolling tank. The rolling tank should be as small as possible, which can speed up the updating speed of the working fluid and reduce the retention 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 high-precision liquid level control. For padding dyeing liquid, use a universal uniform padding car, but it must be equipped with left, middle, and right subdivision pressure gauges to strictly control the padding rate of left, middle, and right, and reduce the color difference between left, middle, and right. Dip The temperature of the rolling liquid should be at room temperature, which should not be lower than 20℃ in winter and not exceed 30℃ in summer. The rolling liquid rate is 85% ± 1%, and the vehicle speed is 24~26m/min. Too fast a vehicle speed will cause the fabric to absorb liquid evenly and make the winding smooth. Unfavorable. Soft water should be used for chemical materials, and hot water with NaP03 dissolved should be washed promptly after padding.
5. Winding
During winding, it is required to use constant linear speed and constant tension center-driven winding. The A-frame enables the cloth surface to 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 a tape of about 20cm wide and 0.2mm thick at the top and bottom. Plastic paper pads are used to eliminate seam and horizontal marks. After the entire roll of cloth is rolled, it must be tightly wrapped with plastic film to prevent moisture from evaporating and contacting the air to cause wind marks. The amount of velvet cloth per roll, regardless of the specification and variety, is generally About 100m long.
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 should be rotated evenly when stacked, and the speed is generally 6 to 8m/min. Since too low temperature will affect the diffusion and dyeing rate of dyes, 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 Accelerating the hydrolysis rate of the dye on the cloth is not conducive to the fixation rate. Therefore, in high-temperature seasons above 35°C, avoid high-temperature times during the day and stack 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
The washing temperature is the order in which the rolls should be rolled on time. Those who roll them first are 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 number:
752 yuan color; production volume 1184m; gray fabric specifications, 9.7/18.2378/402112 weft weight velveteen.
Technical prescription:
Remazo Black B133 6.98kg, Remazol Yellow 3BS 633g, Remazol Yellow 3RS 590g, urea 120g, penetrating agent JFC150g/120L, 38ºBe NaOH 7.95kg, 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 → Soaping (dispersant 5 g/L) 95℃ → Hot water washing 95℃ → Cold water washing → Drying.
Cold pad-batch dyeing is the most suitable dyeing process for cotton velveteen products. Production practice has proved that the use of cold-pad-batch dyeing process Dyeing can improve the first-class rate of finished products and the dye fastness of fabrics.
Afterwords
Cold pad batch dyeing significantly reduces production costs and achieves energy saving and emission reduction benefits. </p
