Department of Textile Engineering

Project Title :Comparison of Batch to Batch Shade Variation Considering Parameters in

Knit Dyeing

SOUTHEAST UNIVERSITY

Name : MAZADUL HASAN SHESHIRID: 2010000400008Batch: 13th Batch (Session 2009-2013)Department: Wet Processing Technology Email: mazadulhasan@yahoo.com (FB)Blog: www. Textilelab.blogspot.comSoutheast University,Bangladesh Department of Textile Engineering

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Shade is the depth of color percentage. Shade is expressed in percentage of dye amount in unit weight of fabric. Shade matching depends on the accuracy of the man's eye. It is a visual process for this reason same shade may have difference comments from different person.

Shade:

It is the variation of shade or depth of color (hue) in same fabric roll or among different batches. In dyed fabric often shade variation is found. Shade variation may occur selvage to selvage, selvage to center of fabric width or one end of the fabric rolls to another end.

Shading or shade variation is considered as one big problem in fabric. A lot of orders are cancelled because of the shade variation between the batches. Though there is a tolerance is given or set , but it is too tough to maintain the exact same shade among all the batches. And here is the success of a Textile Engineer.

Shade Variation

In the area of textiles, the most widely employed method of applying colors is dyeing. Although dyeing process affected by many inside and outside parameters, it is a mature technology during several thousand years. Dyeing is still complicated today to fully understand and control dyeing which is more an art than a science. Besides, it is difficult to monitor but must be dealt with to obtain quality products by control various parameter.

Controlling Parameters in Knit Dyeing

 Machine parameters: Temperature Time Pressure Speed (r.p.m) Stability of machine Dosing Liquor ratio Rinsing

Controlling Parameters of Dyeing Process are mentioned bellow:

Process parameters:

pH Pressure Time Temperature Liquor ratio Water Hardness Recipe Fastness

Chemical parameters: Strength Purity Chemical composition Country of origin Environment

  Material parameters:

Maturity of fiber Count Variation Foreign material Yarn uniformity Weave Plan Fabrics faults

Batch to Batch Shade variation

Dyeing is one of the sophisticated part of the textile production. There are so many reasons behind the batch to batch shade variation. They are given below:

Preparation Stage:

Excessive Heat setting: Heat-setting has effect on dye bond formation on synthetic fiber. Uneven and excessive heat setting can cause shade variation.

Uneven pretreatment: Uneven, improper scouring & bleaching causes shade variation.

Causes of Batch to Batch shade variation in dyeing

Using Chemicals of different concentration: If concentration of input chemical is varied from one batch to another then shade variation is occurred.

Improper color dosing: Improper color dosing can cause shade variation.

Workers’ Negligence: Due to worker’s negligence, shade variation happens.

On process Causes :

Rope length & Cycle time: If rope length is same but cycle time is varied from one batch to another it may cause shade variation. For example, if cycle time of first batch is greater than the second batch results each portion of the loop will not get same time for exhaustion and fixation of dyestuff. So the dye penetration percentage becomes higher for first batch.

Reel speed: Reel speed changes with fabric GSM, loads per nozzle, cycle time etc. which has great effect on shade variation.

Lack of control on dyeing m/c

Running time: Running time is another factor for batch to batch shade variation. Due to the variation of running time of different stage of dyeing, the action of same chemical/dyes, used in different batches also varied from one batch to another batch. This also may cause batch to batch shade variation.

Fluctuation in power & temperature: Fluctuation in power supply and temperature also responsible for variation.

Dyes lot variation: Dyes strength, reactivity etc. properties can vary lot to lot even drum to drum that causes shade variation.

PH: Throughout overall dyeing process, pH has great impact on shade variation. In reactive dyeing, fixation pH is very much important to achieve uniform shade. Every dyestuff appears in different tone under different pH conditions. It has observed that, if pH of polyester dyeing is not within the range, shade will become yellowish, dull etc.

Improper neutralization: If neutralization is not done properly, residual alkali can affect dyeing as well as leads to shade variation.

Soaping: According to the depth of shade; amount of soap, soaping time and temperature can change shade and can make shade variation.

Final cationic fixing operation: Fixation operation can cause shade variation in case of time, depth of shade.

Poor Lab-to-bulk Correlation: If in bulk production same liquor ratio, recipe, chemicals, process stages, runtime etc is not followed according to lab, there is much more opportunities to acquire shade variation as well as other process faults.

Finishing Stage: Not only the preparation and dyeing operations are important, final finishing operation also is very important to avoid batch-to-batch variation.

Softener quality: according to difference in softener quality, strength, nature, concentration, pH etc. shade variation can be noticed during finishing.

Unequal drying temperature: If drying temperature is not equal, shade variation happens.

Follow the standard pretreatment procedure. Standard dyes and chemicals need to be

used. Maintain the same liquor ratio Try to maintain equal loop length, equal

amount of material per nozzle. Maintain the same dyeing cycle. Maintain equal dosing time, runtime Identical dyeing procedure should be

followed for the same depth of the Shade.

Remedies

Make sure that the operators add the right bulk chemicals at the same time and temperature in the process.

Dyes and chemicals strength should be checked regularly.

The pH, hardness and sodium carbonate content of supply water should check daily.

Lab to bulk correlation should be maintained properly.

Equal finishing parameters (drying temperature, softener treatment, squeezing pressure etc.) should be maintained properly.

Remedies