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7 influencing factors for batch to batch shade variation in knit dyeing

Batch to batch shade variation is a common problem in knit dyeing factory. Often dye houses have to pay extra money for the re-dyeing process. Shade variation also costs time which is directly convertible to money. At the same time, the quality of the fabric is also hampered for extra processes.

batch shade variation in knit dyeing

However, by adopting some initiatives this problem may be solved very smartly and effectively. First of all, it is needed to develop a standard operating procedure (SOP) for the dyeing process and should follow the SOP strictly for every batch.

Seven influencing factors-which should be included in the knit dyeing SOP- are described below.

  1. Effects of liquor ratio: Liquor ratio is a leading factor for batch to batch shade variation. If a factory can ensure liquor ratio and a specific gravity of salt then 80% problem will be solved in case of batch to batch shade variation.

Suppose, the 1st batch was dyeing with L:R = 1:8 and 2nd batch L:R = 1:6 then what should be the consequences? The concentration of dyes in case of 2nd bath is more than 1st one which will result in darker shade and this process is vice-versa. So, the liquor ratio should be the same for every batch and this is mandatory.

  1. Specific gravity of salt: Specific gravity of salt should be measured and should take the corrective action against it.
  2. If dyes in the bath: By using specific gravity-meter, measure the specific gravity of salt and check it with the standard values. If gravity is more, water should be added. If sp. gravity is less, then salt should be added.
  3. If dyes are not in the bath: If sp. gravity is more then drain required amount and fill the required freshwater again. If the sp. gravity is less then salt should be added.

Specific gravity chart for gluber salt-

Salt g/l 40 Degree Celsius 45 Degree Celsius 50 Degree Celsius 55 Degree Celsius 60 Degree Celsius
10 1.002 1.00 .998 .996 .993
20 1.011 1.009 1.007 1.005 1.002
30 1.02 1.018 1.016 1.014 1.011
40 1.029 1.027 1.025 1.023 1.02
50 1.038 1.036 1.034 1.032 1.029
60 1.046 1.044 1.042 1.040 1.037
70 1.055 1.053 1.051 1.049 1.046
80 1.064 1.062 1.060 1.058 1.055
90 1.073 1.071 1.069 1.067 1.064

By this process, specific gravity of salt should be controlled. As a result, this will help to reduce batch to batch shade variation.

  1. pH: pH level should be maintained in every bath. The minimum deviation is considerable, but if it crosses +- 0.5 then that will lead batch to batch shade variation. So, to maintain the pH in a similar range Mixed Alkali is the best solution.
  2. Dyes combination: The exhaustion and fixation curve of the dyes should be more or less similar, on the other way it may hamper levelness of dyeing and causes the batch to batch shade variation.
  3. Lot (fiber and dyes): The lot of fiber and dyes should be the same. When it is a big size order, still the same fiber lot should be confirmed. Dyes and chemicals also should be from the same lot.
  4. Pre-treatment: Pre-treatment process for all batches should be same or it will lead to batch to batch shade variation problem.
  5. Recipe: Recipe for the pre-treatment, dyeing and after treatment should be same for all the batches. Though most of the Bangladeshi dye houses are now using the semi-automatic dispensing system.

Here, by building an SOP according to those 7 influencing factors, batch to batch shade variation could be removed and this will increase factory efficiency, profit and reputation also.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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