Purposes, Equipments and Working Process of Dyeing Lab

Dyeing Lab:
Dyeing lab is the heart of the dyeing factory. Lab dip development is done in dyeing lab. We know from the previous article, lab dip is a particular garment style, containing many shades of the fabric color which the buyer is asked have to be sent to the buyer for the approval before going for further production. Higher precision lab can aid easily to achieve the goal of the dyeing mill. 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 tests different equipment’s 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.

dyeing laboratory — Fig: Dyeing laboratory

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

Color match prediction
Color difference calculation
Determine metamerism
Pass/Fail option
Color fastness rating
Cost comparison
Strength evaluation of dyes
Whiteness indices
Reflectance curve and K/S curve
Production of shade library
Color strength

Machine Requirements in Dyeing Lab:

CCM (Computer color matching) Software used: Color i7
AGS Macbeth Spectralight-III
2 Roll laboratory padder [Vertical + Horizontal] by Mathis
Laboratory steamer by Mathis
Dispenser by Tecnorama
Infrared (IR) Lab Dyeing Machine
High Temperature Lab Dyeing Machine
Oscillation Dyeing Machine
Lab Jig Dyeing Machine
GyroWash etc.

List of Tests are Done in Dyeing Lab:
Testing process in dyeing lab are divided in three classes.

Physical Testing
Lab Dip/Chemical Tests
Mechanical Test

1. Physical Tests

GSM
Fiber Diameter
Ends per inch
Linear Density

2. Chemical Tests

PCP
Blend composition
Identification of Textile Fiber
Identification of Dyes
Solvent Extractable matter
Chloride Content
Sulphate Content
pH value of water extract
Moisture Content
Shrinkage to Water
Colour Fastness Tests

3. Mechanical Test

Tensile Strength and Elongation
Breaking Strength
Bursting Strength of Paper
Tear Strength
Elmendorff Tear Strength
Air permeability of Paper
Pilling Test
Dry and Wet Rubbing (Crock Meter)
Ether Soluble Matter
Water Absorbency
Lead and its compounds
Scouring loss
Flammability

Generally below tests are done in dyeing lab:

Dimensional Stability to washing (Shrinkage)
Spirality/Twisting
Colorfastness to washing
Colorfastness to Water
Colorfastness to Perspiration
Colorfastness to Rubbing/Crocking
Colorfastness to Saliva
Colorfastness to Actual Laundering
Print Durability
Fabric Weight
Thread Count
Pilling Resistance
pH Test
Yarn Appearance
Yarn Count etc.

Process flow path of continuous process in dyeing lab:

Spectrophotometer

↓

Dispenser

↓

Dyeing (2 roll laboratory padder)

↓

E-control

↓

Soaping

↓

Dry

↓

Shade checking

*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 (Color: 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:

Spectrophotometer

↓

Dispenser

↓

Dyeing (exhaust process)

↓

Soaping

↓

Dry

↓

Shade checking

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:

Visually in Spectralight (AGS Macbeth Spectralight-III OX-rite)
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

Computer Color Matching (CCM) System:

In computer color matching system, we have to first make an attempt to quantify colors by virtue of a unique reflectance pattern that each color 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 color.
For this, we have to collect the spectral reflectance data for both the standard color and the dyes.

Spectrophotometers in dyeing lab — Fig: Computer color 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

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* = a standard– a sample
b* = b standard–b sample and,
E = (L2 + a2 + b2)1/2

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

*Also the color 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

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.