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Examples of common processes in cold pad batch dyeing

Date:Oct 12, 2020

Examples of common processes in cold pad batch dyeing


        The spandex weft elastic cloth is pad dyed by a long car, which is easy to produce wrinkles. Due to the large radial tension, it will shrink the width and feel hard, which is difficult to meet the requirements of export products. For cold pad-batch dyeing of elastic cloth, X-type or K-type reactive dyes with good reactivity and low-temperature dyeability should be used, or imported remazol dyes. Due to the low reaction temperature, the yarn count is small and the fabric winding is tight. , There is no relative movement between the cloth surfaces. Therefore, the weft direction is not easy to shrink, the fabric surface is dry and tidy after dyeing, and the side lanes are neat, avoiding the occurrence of shrinkage, wrinkles and deep and shallow edges.


    

1 Fabric specifications

Spandex twill 36tex×36tex+7.7tex, 307 pieces/l0cm×157/l0cm; spandex poplin 15tex×15tex+7.7tex, 438 pieces/l0cm×298 pieces/10cm.


2 Process flow

Semi-finished products padding liquid → stacking → washing → soaping → washing → drying → soft stenter (or other finishing) → pre-shrinking.


3 Process conditions

Dyestuffs and alkalis are separately prepared in high-position tanks, and added to the small padding tank at a ratio of 4:1 during padding. The rolling liquid is 25℃, the rolling margin is 70~75%, and the edges are rolled up. 2500~4000m, tightly wrapped with plastic film, then sealed with sealing tape. X-type and Remazol dyes are stacked for 3-6h; when K-type reactive dyes are stacked, the cloth rolls are rotated at 6r/min for 20h; after stacking, they are washed on LMH643 soaping machine.


4 Dyeing prescription

① Purple: Reactive Violet X-2R 14.4 g/L, Reactive Blue X-BR 3.5 g/L, Urea 10 g/L, Soda Ash 15 g/L.

② Orange: Reactive Red X-3B 1.2 g/L, Reactive Bright Yellow X-G 6.5 g/L, Reactive Brilliant Blue X-BR 0.6 g/L, Urea 10 g/L, Soda Ash 10 g/L.

③ Blue: Remazol Black B15 g/L, Remazol Brilliant Red 3BS 0.2 g/L, salt 25 g/L, 32ºBe caustic soda 10ml/L.

④ Brown: Remazol Red 3B 4.5 g/L, Remazol Yellow 3RS12 g/L, Remazol Brilliant Blue BB3 g/L, table salt 30 g/L, 32.5% caustic soda 15ml/L.

The physical indexes in Table 10 are 36tex×36tex+7.7tex×307 pieces/10cm elastic twill as an example. The shrinkage rate of the general pad dyeing process is 2.8-3.4% in the warp direction and 3.6-4% in the weft direction.


In cold pad-batch dyeing, the warp direction is not subject to tension and the weft direction spandex is not subject to the high temperature effect of long car dyeing. Ensure the stability of the door width and the requirements for shrinkage. The spandex elastic cloth is dyed by cold padding, the color is bright and full, which can avoid the color difference and wrinkles on the tip of the head. The process saves energy, saves labor, reduces sewage discharge, and reduces production costs. In the process operation, the accuracy of color imitation is high, which can meet the production requirements of small batch, multiple varieties and fast delivery. The process equipment for cold pad dyeing is composed of a uniform rolling car, a high-level material tank, an lye mixing device, a rolling tank, a rolling liquid conveying pipe and a large coiling machine.


Advantages of cold pad-batch dyeing: Due to the restrictions of environmental protection regulations and the requirements for various color fastnesses, especially dry and wet rubbing fastness, reactive dyes have become the most important dyes in the printing and dyeing of cotton fabrics. The cold pad-batch dyeing process is short, the equipment is simple, the investment is small, the production preparation cycle is short, the energy consumption is low, the fixing rate is high, and the dyeing is uniform. Therefore, reactive dye cold pad-batch dyeing has been rapidly promoted in my country in recent years and has become one of the main processes for dyeing cotton fabrics.


In the production of warp beam dyeing and long-car pad dyeing, the fabric is running and rolling. Therefore, the fabric is easy to run off and produce wrinkles. The pre-treatment dyeing with cold pad pile is mainly because the mechanical equipment is running and the fabric basically does not move or moves less. This can reduce the friction between the fabric and the mechanical equipment, so it can also reduce the possibility of fabric deviation and wrinkles. Velveteen products are more suitable for dyeing by cold rolling process.


(1). Selection of dyes


The Skyzol RGB series dyes of Tiankun Group are currently the most widely used reactive dyes for cold pad-batch dyeing. It is a vinylsulfone reactive dye with duality of ester bond and ether bond. During the dyeing process, vinyl sulfone groups are produced under the action of bases. They also covalently bond with the cellulose hydroxyl group to fix the fiber, which improves the dye uptake rate. Due to the increase in the fixation rate, the dye is not fixed. The reduction in the color fastness of the dyed product has been correspondingly improved. At the same time, Remazol dye has excellent permeability, stable color and good reproducibility, so it is very suitable for cold pad-batch dyeing.


(2). Requirements for padding semi-finished products


a. Due to the characteristics of the wool direction of the velveteen, the semi-finished products must be separated from the upper and lower widths into rolls, and the hair direction should be straightened. The hair direction of each curl is the same.


b. The semi-finished product has a hair effect of 14cm/30min or more, and all parts are uniform.


c. The cloth surface temperature is cooled to room temperature, and the moisture regain is uniform. For semi-finished products that are boiled and bleached the next day, the outer layer should be covered with a head cloth to avoid a large difference in moisture regain between the inner and outer layers of the cloth pile. Especially in the rainy season, it is best to dry and cool properly before padding to ensure consistent moisture regain.


d. The seam joint must be flat seamed with cotton yarn and wool three-thread overlock, the seam is flat and straight, there must be no folds, and the cloth edges are neatly butted.


(3). Process prescription


Dye X g/L, urea 100 g/L, penetrant 1~2 g/L, NaOH (38ºBe)Y g/L, Na2Si03 (40ºBe) 32 g/L. Dye and NaOH dosage (g/L)


Among them, urea has the function of solubilizing and puffing fibers, and NaOH provides enough alkalinity for dye reaction and fixation. Although Na2Si03 also provides a certain alkalinity, it mainly acts as a buffer and can adjust the pH value of the lye. It can improve the stability of the working fluid, alleviate the hydrolysis of the dye, and improve the fixation rate; The side plays a protective role and can absorb the CO2 in the air at the edge of the cloth, thereby maintaining the concentration of NaOH in it, so that the edge of the cloth is fully fixed, and preventing the occurrence of deep, medium and shallow edges.


(4). Pad dyeing liquid


In order to slow down the hydrolysis of the dye in the strong alkali and stabilize the dye solution, the padding working solution is separately dissolved by the dye and alkali agent, and the dye solution and the lye solution are mixed in a 4:1 ratio through a proportional pump and then injected into the padding tank. The padding tank should be as small as possible to speed up the renewal 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 is sufficient for 30L, but it must be equipped with a high-precision level controller and padding dyeing solution. It is sufficient to use a universal uniform rolling cart, but it must be equipped with a left, center, and right subdivision pressure gauge to strictly control the rolling rate of the left, center, and right to reduce the color difference of the left, center, and right. The temperature of the padding liquid is at room temperature, not lower than 20°C in winter and 30°C in summer. The rolling rate is 85% ± 1%, and the vehicle speed is 24 to 26 m/min. Too fast speed is not good for fabric absorption and evenness and smooth winding. The chemical material should be soft water, and it should be cleaned with hot water dissolved NaP03 in time after padding.


(5). Rolling


When rolling, it is required to use constant linear speed and constant tension center to drive the winding A-frame, so that the cloth surface can be wound smoothly from beginning to end, without any additional friction, to ensure that the inner and outer layers of the cloth roll are uniform and consistent. When encountering seam joints, use plastic paper with a width of about 20cm and a thickness of 0.2mm to padded the top and bottom of the seam to eliminate cross-stitch marks on the seam head. After the entire roll of cloth is wound, it should be tightly wrapped with a plastic film to prevent moisture evaporation and air contact from causing wind marks. The volume of each roll of velveteen is generally about 100m long regardless of the specifications.


(6). Stacking


In order to prevent the dye liquor from oozing and depositing in the cloth rolls, causing color difference between the upper and lower layers, the rolls must be rotated when they are stacked, and the speed is generally 6-8m/min. Because too low temperature will affect the diffusion and dyeing rate of dyes, When the room temperature drops below 20°C, heat preservation measures must be taken, and cloth curtains can be used in the workshop for proper heating. When the room temperature is too high, the hydrolysis rate of the dye on the cloth will be accelerated, which is not conducive to the fixation rate. Therefore, in the high temperature season above 35 ℃, high temperature during the day should be avoided, and stacking at night and morning should be used as much as possible. The stacking time is theoretically more than 6h, but in order to ensure the uniformity of the dyeing, it is generally stacked for 12-24h. Even if it is extended to 48h, it will not affect the shade and depth of the dyeing.


(7). Wash


The washing temperature is the order of rolling the rolls on time. The first roll is washed first. According to the characteristics of velveteen, first unwind and then wash, to ensure smooth hair into the machine, washing can be performed on ordinary dry cleaning machines. Washing can be carried out in 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 that the cloth surface is neutral and the PH value is below 8. If it is dyed in deep and dense colors, the cloth surface is not neutral, you can add HAc1~2g/L to wash.