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Eliminating or minimizing white spot on dark shade

Abstract

In this project, we aimed to determine the root causes of it as well as take precautions necessary to defend this, take a step to rectify if occurred. The project, named “Eliminating or minimizing white spot on the dark shade”, has taken 9 reputed garments/textile factories to address this dyeing problem properly. As a team, we worked to solve dyeing issues of black color on several types of fabric such as Single jersey, Lycra single jersey, Rib, Fleece, etc.

Available data, industrial practices other relevant matters were analyzed properly to form a standard and do a trial based on it. After that, a standard is formed by which we can minimize, in some cases eliminate this problem. Through this research initiative, the dyeing section can see a positive return out of this project work hopefully.

Keywords: Dyeing fault, Spot problem, Causes, Process development, Best practice, Quality control, Problem rectification, SOP.

Introduction

Dyeing, a very critical as well as very important section for the textile industry usually faces some problems. The four remarkable problems include “White spot” whereas the other three are uneven dyeing, Shade variation, Crease mark. Color spot, Oil spot, Color missing, etc don’t belong to the White spot problem. Our central and intensive main concern goes for only dark shade.

This problem is addressed as a soda spot or softener stain in Dyeing QC. But only soda or softener isn’t accountable for this. This problem has logical possible causes too.

Causes accountable for it

This problem is visual in the upper fabric surface but creates a very strong bond or weak bond with cellulose.

Some problems are marked as major while the others are minor. Major ones are such as:

  1. Higher hardness.
  2. Higher PH.
  3. Higher foam during unloading & after unloading from machine 24hours to above time waiting for dry.
  4. Improper mixing of softener, soda, chemicals. Improper filtering and too fast dosing of them by the operator.
  5. Pressure marks created from machines due to entanglement of sewing threads, versatile dirt.
  6. Sedimentation (creates via detergent + anti-creasing agent +sequestering agent), Polyester oligomer and residual salts in the inner dyeing machine surface.

On the other hand, we also mark some problems as minor but cannot be ignored at all. They are listed below:

  1. The pressure of CaCO3, Mg2+ on the fabric surface.
  2. Soda impurities or contamination or presence of sodium and calcium silicate on machine surface.
  3. If the wash is not proper residual salt exists.
  4. Sizing materials poor quality.
  5. Excessive force when pulling fabric
  6. Presence of silicon and silicate ligands.

Location and seasonal view

7 reputed factories “from two different districts and different individual thanas” 12 consecutive months data are analyzed this time. Then their total defect% is calculated. Factory-wide total defect varies from 6% to 11%. & How many defects are occurred (in percentage) in dyeing section compared to total defects and how many defects are occurred as white spot compared to defects in dyeing section (in percentage) are shown in this chart below:

Factory Name (symbolic) Zone Defects found in dyeing section

(Among total defects)

Contribution of white spot problem

(Among total defects)

Contribution of white spot problem

(among dyeing problems only)

F1 Gazipur 8.86% 0.83% 9.36%
F2 Gazipur 15.88% 0.95% 6.23%
F3 Gazipur 9.38% 0.97% 10.52%
F4 Gazipur 10.49% 0.85% 8.13%
F5 Dhaka 15.52% 0.97% 6.28%
F6 Dhaka 11.88% 0.59% 4.98%
F7 Dhaka 12.12% 1.25% 10.33%

Here we find an important thing is that no zonal diversity facts to create White spot problem as well as any type other dyeing problem. And why this problem is called one of the four major dyeing faults is illustrated via a chart given below:

Four-dyeing-faults-illustrated
Figure 1: Four major dyeing faults are illustrated via a chart.

Among all of these 9 factories, the ratio of the defect in the dyeing section is illustrated in this chart which reminds us of the four most common dyeing faults. Thus no doubt remains to say the “white Spot “problem is a huge threat. But headache is even higher because of being causing mainly in the darker shade especially black. If we calculate this problem for darker shades the ratio is even higher.

Name of month Percentage of white spot problem (only for black shade)
January 6.42%
February 6.46%
March 13.34%
April 18.59%
May 17.68%
June 14.33%
July 11.22%
August 12.22%
September 11.56%
October 10.86%
November 9.72%
December 10.13%

9.16% of this problem is occurred by white spot at an average mentioned on the previous pie chart. But here only for black shades, we find this even higher. And another additional fact is that in hot-tempered month, factory faces more problems and in low-tempered month factory faces relatively fewer problems.

Precaution

This problem must be faced from the very beginning of the dyeing operation, in some cases before dyeing. Every precautionary step will be done based on the causes for it. Those precautionary terms are formed as the probable best practices:

  1. Hardness below 15 ppm.
  2. Controlling core PH very strictly. PH value of water, softener, soda, sequestering, agent, solution, the solution must be closed and must have a PH less than 7. Controlling PH 4-5 in padder.
  3. Demineralization for removing fabric hardness & Proper neutralization before dyeing. A core neutralizer may be used.
  4. Increasing sequestering dosing on scouring bath. And Neutral sequestering agent on dye bath, acidic sequestering agent as leveling.
  5. Ensuring compatibility on every step.
  6. Unload fabric on a slightly acidic medium with water to avoid foam. The fabric will be dried within 12 hours.
  7. Maintain machine wash with wastage fabric as per the given schedule.
  8. Proper filtering of soda, proper mixing of softener, Proper softener dilution.
  9. Fill acid on cycle wash properly & proper wash at bath drop at (60-70)0C acid wash.
  10. If the softener is used on dye bath antifoaming agent must be used.
  11. A multifunctional leveling agent is used.
  12. Saturated auto steaming.

Method

Based on the deep, logical, scientific studies, we trialed 481kg fabric to dye black.

Some of the variables were as

  • Controlled: Hardness, Clean machine, pH, soda and softener purity
  • Dependent: Foaming, padder pH, sedimentation.
  • Independent: Pressure mark, an entanglement of sewing threads, dust, presence of permanent hardness, rubbing in the fabric nozzle.

Some information taken from the recipe relevant for the experiment are given below:

  • M: L – 1:7
  • Sequestering agent – 0.5 g/L
  • Surfactant (Anionic) – 1.5 g/L
  • Emulsifier and Scouring agent – 1.0 g/L
  • The enzyme (acidic) – As it is
  • Salt – 2 g/L
  • Soda – 3 g/L
  • Softener – As it is
  • pH – 5.7-6.0
  • Temperature – 60 +/- 5 (degree Centigrade)

Softener used for a batch in the exhaust and for the other batches softener used in the padder maintaining a pH 4-5. The cycle time used as experiment 110-120s to tempt the machine to create more foam and some antifoaming agent used.

After unloading the QC report was checked and assessed. Then the proper decision was taken based on them.

Results

The result was fairly good from the Dyeing QC report. We know every industry faces direct or indirect loss at 0.4%-3.5% rejection occurred by garments and fabric for this white spot problem. And the white spots on the fabric surface occur generally 9-25times per 100kg on average.

The databases taken from different industries, white spot factors are known such as:

Number of White spots per 100kg Fabric Rejection for it (directly or indirectly)
0-4 0%
5-9 0%-0.3%
10-16 0.6-1.5%
17-25 1.6-1.8%
more than 26 Can’t be determined. It’s huge.

# This table is trustworthy or very close to trustworthy. Because other many a lot of factors are accountable for too in 4 point system. Less than 1% is acceptable.

The white spots per 100 kg on trialed batch are less than 7.

So that, there’s no possibility to face bad points from 4 point system as well as rejection accountability for it. Or, a little possibility may remain. Thus the process of controlling told as precautions are fruitful enough to solve this problem and the probable causes are scientifically logical enough. Although if a problem occurs again, then we have precautions for it.

white-spotted-fabric-swatch
Figure 2: white spotted fabric swatch.

Discussions

  • In the summer season, the possibility to have metallic and non-metallic ion is more as the water lowers down. Then the hardness should be decreased 10% of the control point that’s industrially 15ppm at high. And if permanent hardness is found on the water of that area there should be some factors there. Then demineralization is needed must. And softener should be used in padder maintaining a pH 4-5.
  • If the machine is new we can decrease cycle time. But there should be a possibility to create more foam. Then we should increase the antifoaming agent. . And sometimes foam is more without magnet reason. Then we should unload the fabric with a lot of water.
  • Soda and softener filtration must be good. Core pH of all chemicals, ingredients, solution should be maintained and if we want to do that directly then a core neutralizer is used.
  • If the raw fiber is not so good or permanent hardness found on the water, then demineralization should be used or surface cleaning agents should be used.
  • Proper machine cleaning should be maintained very strictly on regular terms with wastage fabric on slightly acidic medium terms. Skilled operators are preferred here.
  • If this problem occurred then rewash with acid is needed. If the problem is more then re-wash should be done with enzyme on acidic medium.

Moreover, if we can control this white spot problem, then some other problems are also vanished or minimized. (Shown on the table)

Fabric weight white spot number per 100kg color spot number per 100kg pinhole number per 100kg Oil stain number per 100kg
1000 9.4 2.2 1.3 1.1
880 10.45 2.16 1.82 0.91
672 11.49 1.49 1.64 2.53
481 (trialed) 6.81 00 0.42 00

On trialed batch, we found some other problems are solved too as a bonus. So that there remains no other doubt for this process controlling points told as a precaution. This must develop a better business impact both directly and indirectly.

Rectification

As this is a total floor-based industrial operation, this problem may occur anytime. Then we have to take steps to solve this for achieving healthy quality remarks. Any of these points mentioned below is fair enough to rectify the white spot.

  1. Light enzyme with a sequestering agent for 55 min. (for less problem)
  2. Steeping to full rectification. (for more problem)
  3. Refinish with acid than light enzyme with a sequestering agent. (for less problem)
  4. Detergent wash. (if a problem occurred by foam. It can be understood if the spot fades after water spraying.)
  5. Acid wash after soda dosing against softener mark. (if expertise body confirms those as softener marks)
  6. Steeping + re-mercerize.

Conclusion

The research is done based on deep studies of the dyeing section both theoretically and practically. Then topic narrowed down on this “White Spot “on the dark shade. That was done with turning or back sewing so that spot may occur on the backside. But in most cases, the spots float themselves.

Moreover, it isn’t a standard operation. So that deep studies on this problem is also done. After proper supervision industrially and academically the most three keynotes are formed called CAUSES, PRECAUTIONS, RECTIFICATION.

We have done a successful major trial and assessed other batches done based on this standard medium we came to this confidence with some important discussions. This article is made based on the aforesaid research. Finally, it can be said that this may be a way to add a new transformation in the dyeing section of textile industries.

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

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