The cold pad-batch dyeing process is between exhaust dyeing and continuous dyeing. It is a semi-continuous dyeing process. It has obvious energy saving, dye saving and great production flexibility. It is especially suitable for the production of small batches and multiple varieties. According to foreign statistics in the 1990s, the proportion of cold pad-batch dyeing in the reactive dye dyeing process has increased to 20%. The most widely used cold pad-batch dyeing process is the short-time cold pad-batch method.
Cold pad batch dyeing technology
1. Short-time cold rolling Preparation method (KKV)
Due to the use of a liquid mixing device, the dye liquid in the process is stable and easy to control, so the stacking time can be shortened accordingly, and the process flexibility is high, and the liquid mixing is It is easy to change colors, and one cloth roll can be dyed with multiple colors or varieties.
The short-term cold padding equipment is equipped with a metering and mixing device for dye liquor and alkali liquor. The dye and alkali agent are prepared separately, and are continuously mixed in the device, and added during padding. In the padding tank, the mixing ratio is 4:1, that is, 4 parts dye to 1 part alkali agent. This method can use a larger amount of alkali to accelerate color fixation and ensure sufficient stability of the dye solution. It can slow down the hydrolysis of reactive dyes in stronger alkali agents and reduce the color difference before and after processing.
Alkalis and dyes prepared separately must not be mixed prematurely in the mixing device before padding. Padding fluid cannot be injected into the rolling tank too early. The fabric must be cooled before entering the rolling tank. A small rolling tank and high process speed are used to ensure rapid replenishment of the dye liquor and keep the working fluid fresh. These methods are all effective measures to reduce dye hydrolysis.
2. ME type reactive dye cold pad batch dyeing process
Reactive dyes used for cold pad batch dyeing require high reactivity and hydrolysis stability, can complete the fixation reaction at room temperature, and have a high fixation rate. The reactivity of ME-type reactive dyes is between X-type and K-type, and the hydrolysis resistance stability is far better than that of X-type and K-type reactive dyes. Therefore, ME type reactive dyes are completely suitable for cold pad-batch dyeing of fabrics.
Some people have done the following experiments. Fabric specifications: 15tex×15tex, 523×283 mercerized cotton poplin, when the dye concentration is 20g/L, the alkali agent NaOH (36°Bé) 15mL /L, Na2SiO3 (40°Bé) 150mL/L; stacking time 8~12h. Applying the above process, reactive yellow M3RE, red M3BE, and blue M2GE can achieve three primary colors in cold pad-batch dyeing production; the dye yield is high, the dye liquor stability is good, the cloth surface has good level dyeing and dyeing through, and the dye fastness All meet national standards.
3. Cold pad-batch dark dyeing process with remazo dyes
The reactive cold pad process for medium and light colors of pure cotton has excellent results. However, for dark colors, especially black, the domestic reactive dyes are not dyeing deep enough, and the fastness cannot meet the standards. There is information stating that the cold pad batch dyeing of dark colors using the original remazolin reactive dyes of the German Hoechst Company has been successful, and the dye fastness indicators have all reached the standard.
Fabric specifications: pure cotton 30tex×30tex semi-bleached mercerized cloth, semi-finished product singeing grade 3.5, wool effect T6.2cm, W5.6cm, pH7.
Process flow: semi-finished product → cold pad batch dyeing → washing → soaping → washing → drying.
Process prescription:
Dye remazolin deep black N150
Dye concentration 80g/L
LCS penetrant 3mL/L
Water glass 100mL /L
Caustic soda 84mL/L
Process conditions ：
The workshop temperature is 25℃
The rolling residue rate is 70%
The vehicle speed is 60m/ min
Stacking time 16h
Washing : Cold water washing → warm water washing → boiling water washing → cold water washing →Dry.
Notes
1. Mixed alkali solution
A mixture of sodium silicate and caustic soda is used as the alkali solution in the cold pad batch dyeing process. This mixed lye solution provides the best color yield. Caustic soda ensures the alkalinity of the mixed solution, while sodium silicate has an obvious buffering effect, which significantly improves the stability of the pad dyeing solution without damaging the fixation rate. In addition, sodium silicate has emulsifying and colloidal protective properties, which can protect the fabric from being eroded by acid gas and carbon dioxide in the air; it also has an excellent protective effect on the edges of the fabric.
The pad dyeing solution must use soft water, because hard water will cause sodium silicate to form insoluble matter and stick to the roller. A layer will inevitably form on the surface of the roller after drying. Sodium silicate film, so the surface of the drum often needs to be rinsed with cold water. If a certain amount of sodium silicate remains on the drum, as time goes by, the dirt will increase and eventually silicide will be formed. The improvement method is to rinse the drum with hot water after padding. But a more effective way is to use hot water containing sodium tripolyphosphate and a brush to remove it.
2. Semi-finished product temperature
Fabric pre-treatment, drying and rolling The temperature of the dyeing solution should not be too high, otherwise the cloth temperature will affect the stability of the pad dyeing solution. The semi-finished product must be cooled to room temperature before use. A ventilation rack can also be added in front of the cold rolling pad to help cool the fabric.
3. Fabric coiling
The coil after rolling The edges must be aligned to avoid dark and light edges; the seams of the fabric should be overlocked, and the seams should be made of the same material as the fabric, with fine stitches to avoid seam marks and rungs; it should be used when rolling up many types of dyed fabrics with different colors. Separated by plastic film; the stacking process is the same as the cold rolling stack pre-treatment, and the cave is pushed to rotate at a low speed of 4~8r/min.
Economy of cold pad batch dyeing
Two-phase padding SteamThe dyeing method is a traditional dyeing method, often referred to as the pad steaming method. This is the most important process for using remazo dyes worldwide. Especially in the United States, the pad steaming method is used to dye remazolin, and the liquid dye series has been promoted on a large scale.
The process flow: semi-finished product → pad dyeing solution → drying → padding chemical solution → steaming → washing → soaping → washing → drying.
Compared with the cold pad-batch dyeing process, this process has a very prominent shortcoming that it includes intermediate drying and steaming that consume a lot of energy.
The comprehensive cost analysis of various dyeing processes is as follows: taking the cold pad-batch method as 100%, then the two-phase pad-steaming method is 125%, and the thermosetting method is 125%. The jig dyeing method is 118%. The cost of rope exhaust dyeing is twice as high as that of the cold pad batch method due to the large liquor ratio and low color yield. One unit uses cold pad-batch dyeing of towels instead of the original jig dyeing process, which can save 15,000t of water, 3×10^4kW·h of electricity, and 1,800t of steam every year.
The cold rolling batch process is simple, easy to implement and reliable to use. The fabric is padded with dye and alkali solution and rolled. The fixation reaction of the dye is carried out while being rolled into a roll and stacked at room temperature while rotating slowly. After stacking, perform regular water washing to remove unfixed dye. Process equipment, energy consumption and labor costs are lower. Compared with the intermediate drying process, there is no danger of dye migration. The dye penetration is excellent even on heavy fabrics and the color yield is very high.
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