Sunday, July 29, 2018

Dyeing Lab: Purposes, Equipments and Working Procedures

Dyeing lab:
Dyeing lab is the heart of the dyeing factory. Higher precision lab can aid easily to achieve the goal of the factory. Before bulk production a swatch of fabric test dyed to hit a color standard. It is a process by which buyer's supplied swatch is matched with the varying dyes percentage in the laboratory with or without help of spectrophotometer. For doing all test different equipments are used in dyeing lab. In this article I will discuss different aims of dyeing lab, working process of dyeing lab and also different types of machines those are used in dyeing lab.

Aims or Purposes of dyeing lab:
The main aim of dyeing lab is:

  1. Color match prediction
  2. Color difference calculation
  3. Determine metamerism
  4. Pass/Fail option
  5. Color fastness rating
  6. Cost comparison
  7. Strength evaluation of dyes
  8. Whiteness indices
  9. Reflectance curve and K/S curve
  10. Production of shade library
  11. Color strength
Machine required in dyeing lab:
  1. CCM (Computer color matching) Software used: Color i7
  2. AGS Macbeth Spectralight-III
  3. 2 Roll laboratory padder [Vertical + Horizontal] by Mathis
  4. Laboratory steamer by Mathis
  5. Dispenser by Tecnorama
Process flow path of continuous process in dyeing lab:
continuous process in dyeing lab
Fig: Continuous process in dyeing lab
*For CPB process after padding it is dried in hot air oven at 60°c- 120°c for 30 min. After 2- 3 seconds of fixation soaping is done followed by drying and shade checking.

Recipe for continuous process:

  • M:L = 4:1 (Colour: Chemicals)
  • Soda= 12gpl
  • Ceragel (wetting agent)= 2 gpl
  • Anti- migrating agent (MIP)= 10 gpl
  • Resist salt= 5 gpl
Working process in dyeing lab:
  • The standard fabric is checked in the spectrophotometer, which gives us a prediction recipe.
  • According to the prediction recipe dyes are prepared in a dispenser.
  • Then the caustic and chemicals are added to the dye and mixed properly.
  • After that the fabric is padded through the roller.
  • After dyeing the sample is dried at 120 C for 2.44 min(the temp & time depend on the fabric quality) in a e-control.
  • Then the fabric is washed in soaping machine and dried by iron.
  • After that the dyed fabric is compared with the standard fabric in spectra light and spectrophotometer.
Process flow path of exhaust process in dyeing lab:
exhaust process in dyeing lab
Fig: Exhaust process in dyeing lab
Recipe for exhaust process:
  • MLR=1:10
  • Dye used= (Wx P)/C
            Where, W= weight of fabric
            P= Shade%
            C= Concentration of solution

  • Glaubers salt= 50gpl
  • Soda= 200 gpl
Machine used: Mathis

Machine speed: 50 rpm

Procedure for dyeing:

  • Fabric is put inside the tumbler with dye and salt for first 15 minutes at room temperature.
  • Then after the temperature reaches 60°c half of the soda is added and rotated for 45 minutes.
  • Then again other half of soda is added and rotated for 10 mins.
  • In this way it took total 70 minutes for dyeing of cotton.
After dyeing the fabric is checked for shade variation. It can be done through two ways:
  1. Visually in Spectralight ( AGS Macbeth Spectralight-III OX-rite)
  2. Or in CCM using Color i7 software.
Spectralight has 6 lighting arrangement, according to sunrays received by Earth:
  • Daylight 65 (D65)
  • Horizon
  • TL83 U30 (used for HNM)
  • A10 (used for INCA)
  • UV
  • In computer colour matching, we have to first make an attempt to quantify colours by virtue of a unique reflectance pattern that each colour exhibits and then match this unique pattern by a blend of various dyes.
  • The blend that gives an identical reflectance pattern is an exact match for the desired colour.
  • For this, we have to collect the spectral reflectance data for both the standard colour and the dyes. 
Computer colour matching by spectrophotometer
Fig: Computer colour matching by spectrophotometer
This data is then to be analyzed by using Kubelka-Munk equation:
  • K/S= [(1-r)2 / 2r]
  • Where r is the reflectance value of samples at a given wavelength,
  • K/S= color strength
The basic three things of CCM are:
  • Color measurement instrument (Spectrophotometer)
  • Reflectance (R%) from a mixture of dyes
  • Optical model of color vision
lab system

This model gives us the L* a* b* value, from which we can calculate c*, h* and E.

Where, L*= L Standard – L Sample

a* = astandard– asample
b* = bstandard–bsample
and, E = (L2 + a2 + b2)1/2

*If Eis more than 1, then the result is declared as fail or the recipe is rejected.

*Also the colour strength must be ±100, or else the recipe is rejected.

For example:

  • We have dyed a lab-dip using Jakazol dyes in e-control process.
  • Shade name: STD NAVY
  • Prediction recipe:
            Jakazol Yellow CE= 4.50 gpl
            Jakazol Red CE= 13.50 gpl
            Jakazol Blue CE= 23.00 gpl