Department of Textile Engineering

Topic: Dyeing method &mechanism

Prepared by: Anikdeb

Batch: 17th

Organogram of knit Dyeing Section

General Manager (GM)

Asst.General Manager (AGM)

Manager (Dyeing)

Senior Production Officer (SPO)

Production Officer (PO)

Dyeing Master

Shift in Charge

Floor in charge

Supervisor

Operator

Helper

What is Dyeing

Dyeing is the process of adding color to textile products like fibers, yarns, and fabrics. Dyeing is normally done in a special solution containing dyes and particular chemical material. After dyeing, dye molecules have uncut chemical bond with fiber molecules. The temperature and time controlling are two key factors in dyeing. There are mainly two classes of dye,  natural and made. The primary source of dye, historically, has generally been nature, with the dyes being extracted from animals or plants. Since the mid-18th century, however, humans have produced artificial dyes to achieve a broader range of colors and to render the dyes more stable to resist washing and general use. Different classes of dyes are used for different types of fiber and at different stages of the textile production process.

What is dyestuff

Dyestuff is organic or inorganic substances which can absorb light and reflect some lights to show color. Actually, the dyestuff is water soluble substances. 

Criteria for a Suitable Dyestuff 

Cheap Non-toxic Compatible to other dyes and chemicals High color strength Better brightness Better fastness Good levelness on the materials

Classification of dyestuff

Dyestuffs can be classified according to three ways:-

1. According to common parent structure2. According to application3. According to the nuclear structure

According to the nuclear structure there are two types of dyestuff

1. Cationic Dyes

2. Anionic Dyes

General classification of dyestuff

Classification according to common parent structure or Chemical classification of dyes:  

The chemical constitution of dyes are varied that it is difficult to classify them into distinct groups. The color index classifies dyes as shown. 

1. Nitro dyes.2. Nitro so dyes.3. Azo (Monazo) dyes.4. Azoic dyes.5. Stilbene dyes6. Tgri0aryl methane dyes.7. Xanthenei dyes.8. Quinoline dyes.9. Methine dyes.10. Acridine dyes.11. Nitro dyes.12. Sulphur dyes.13. Thiazole dyes.14. Thizine dyes.15. Indamine dyes.16. Oxazine dyes.17. Azine dyes.18. Lectone dyes.19. Anthra quinine dyes.20. Indigoid dyes.21. Phthalocyanin dyes. 

Classification according to Application of dyes:  

1. Basic dyes2. Acid dyes3. Direct dyes4. Reactive dyes5. Sulfur dyes6. Premetallized dyes 7. Azoic (Napthol) dyes8. Disperse dyes9. Vat dyes  

Application of dyes according to fiber:

Group Application

Direct Cotton, Cellulosic and Blends

Vat dyes Cotton, Cellulosic and Blends

Sulphur Cotton, Cellulosic fibers

Organic pigments

Cotton, Cellulosic, Blended Fabrics, paper

Reactive cellulosic fibers and fabric

Dispersed dyes Synthetic fibers(polyester,nylon,acrylic)

Acid Dyes Wool, Silk, Synthetic fibers, leather

Azoic Printing inks and pigments

Basic silk, wool, cotton

Oxidation dyes Hair

Developed Dyes Cellulosic fibers and Fabric

Modernt Dyes Cellulosic fibers and Fabric, Silk, Wool

Fluorescent Brighteners

synthetic fibers, leather, cotton, sports goods

Mechanism of Dyeing: The process of dyeing may be divided into three phases,

1. Adsorption of dyestuff at the fibre surface2. Diffusion of the dyestuff through the internal structure of the fire, and3. Fixation or anchoring of the dye molecule at a suitable location or dye site.

Adsorption: In the first phase or step the dye molecules in the dye bath move towards the fibre and those that are nearest to the fibre get adsorbed on to the fibre surface. They form a very thin layer of

molecules on the fibre surface. Other dye molecules still in the dye bath can be adsorbs only if this adsorbed layer moves further into the fibre.

Penetration: In the second step, the adsorbed dye molecules enter the fibre structure and gradually penetrate or diffuse into the pores or canals in the structure. The rate of penetration and the depth to which they get will depend upon the molecular characteristics of the dye, the molecular arrangement in the fibre and the dyeing conditions. Diffusion or penetration of dye in the fibre accounts for almost the whole of dyeing time. The greater the penetration of dye into the fibre the brighter and better is the dyeing. Good penetration is thus the key to quality dyeing. Poor penetration results in dull, surfacial dyeing with unsatisfactory colour fastness properties.

Fixation

Fixation of dye means the reaction of reactive group of dye with the terminal -OH group of fiber & thus forming strong covalent bond with fiber. Controlled by maintaining pH by adding alkali properly. Dye and fiber bonding create by four way

1. Van der waals’ bonds2. Hydrogen bonds. 3. Salt linkage. 4. Covalent bonds, etc.

Textile Chemicals Categories and Subcategories   : From pretreatment of textile to its finishing, there are various categories and subcategories of textile chemicals:

1.Pretereatment Chemicals:scouring agents, low foam scouring agents, wetting agents, low foam wetting agents, sequestering agents, mercerizing agents, peroxide stabilizers, peroxide killers, neutralizers 

2.Textile Dyeing Chemicals:Solubilizers & dispersents, levelling agents, soaping agents, dyeing agents.

3.Dyeing & Printing Chemicals:vat levelling agents, thickeners, binders, stain removers, anti back staining agents

4.Finishing Chemicals:cationic softeners flakes/ paste, nonionic softeners flakes/ paste, anionic softeners flakes/ paste,

reactive softeners, cold water soluble softener flakes

5.Antistatic Agents:spin finishes, spinning aids

Some Basic function of chemical used in dyeing section:

 

Chemicals & Auxiliaries

Commonly Used Chemical With its Trade Name

Function

Solublizing Agent

Urea Increase the solubility of dyes

Controls the sublimation at high temperature

Reduction Inhibitor

Lyoprint RG or Resist Salt

Mild oxidizing agent controls the reduction of dyes at high temperature or during steaming.

Alkali Caustic Controls the rate of reaction between dyes and cellulose or in other words it is used for fixation of Reactive Dyes.

Soda Ash Controls the rate of reaction between dyes and cellulose or in other words it is used for fixation of Reactive Dyes.

Increases the fastness properties if used in washing

Sodium-bi-Carbonate Controls the rate of reaction between dyes and cellulose or in other words it is used for fixation of Reactive Dyes.

Binding Agent Helizarin Binder ETS Use as an adhesive to fix the pigment dyes on cotton fiber at high

Chemicals & Auxiliaries

Commonly Used Chemical With its Trade Name

Function

Imperon Binder MTP temperature.

Wetting Agent Cibaflow Pad

Kieralon A

Sandozin EH

To increase the wet ability of fabric and penetration of dyes in the fiber.

Dispersing Agent

Setamol BL

Setamol WA

Dispersogen P

Used for dispersing of disperse and vat dyes.

Antifoaming Agent

Antimusol SF

Leonil KS-U

Used to prevent formation of foam during stirring or during dyeing in one bath.

Anti-migrating Agent

Irgapadol MP

Size CA

Alginate

Emigen AS-U

Increases the viscosity of dyeing liquor to protect migration of dyes under high temperature.

Electrolyte Glauber Salt Decreases solubility of dyes in liquor, Increases affinity between dyes and fiber under moist condition

List of chemicals used in keya knit composite Ltd:

Multi function agent IMEROL BLUE LIQ

Basic Chemicals: Acetic Acid, Hydrochloric Acid, Sulphuric Acid Caustic soda, Formic acid, Bleaching powder.

Detergent & Scouring agent LUBRISCOUR BD, CAUSTIC SODA

Leveling Agent OXINOLL ALL,   LEVAGAL DLP.

Salt Glauber Salt, Common Salt

Fixing Agent MATFIX VNFA LIQUID, ALBAFIX ECO

Per-oxide Killer BACTA SOLAP

Anticreasing Agent EURO LUBE CONE, TEXPORT D-600

Enzyme RETRO CELLPLX, BIO-C35

Bleaching Agent ( 50% )H2O2

PH Controller Acetic Acid

Softener SOULBIO FD, GRAMAZIN-E2R

Terms and definition of dyeing:

1. Shade:

Depth of color %

Light shade- 0.5%

Medium shade- 1.5%

Deep shade-1.5 and above

2. Substantive:

Substantive dye is a dye used in a process in which dye molecules are attracted by physical forces at the molecular level to the textile. The amount of this attraction is known as "substantively": the higher the substantively the greater the attraction of the dye for the fiber. Substantive dyes work best on textiles with high contents of fibrous cellulose and are set in a slightly basic or neutral environment at high temperatures close to boiling point. Substantive dyes are set by hydrogen bonding.

3. Affinity: Affinity means the attraction of dyes to the textile materials is called affinity. It’s related to heat or temperature.

4. Absorption: When dye molecules come to the surface of the fiber, it is called adsorption.

5. Sorption: When dye molecules enter into the fiber it’s called sorption.

6. Desorption: The process by which the dye molecules come out form the inner side of the textile materials in particular conditions it’s called desorption.

Dyeing Machine of Keya Knit Composite Ltd:

Machine Type Machine Quantity Total Brand/Country of

Capacity/Batch in Kgs (Sets)

Capacity/Batch in Kgs

Origin

Vertical Winch (Computerized)

200 3 600 Fongs (China)

400 3 1,200Fongs(China)

400 1 400 Fongs (China)

Working Process of Winch Dyeing Machines:

Dyeing Method On Winch Dyeing Machine:

The basic principle of all winch dyeing machines is to have a number of loops or ropes of the fabric in the dye bath, these ropes are of equal length, which are mostly immersed in the liquor in the bath. The upper part of each rope runs over two reels which are mounted over dye bath. At

the front of the machine, above the top of the dye liquor, is a smaller reel, which is called jockey or fly roller. The fly roller remains freewheeling along with fabric rope. At the back of winch tank is the winch wheel, which pulls the fabric rope from the dye bath over the jockey reel for dropping in the dye bath for immersion. From the dropped location, the fabric rope travels back. To be lifted and fed to winch wheel. The dyeing process on winch dyeing machines is based on higher M: L as compared with other dyeing machines. The process is conducted with very little tension. The total dyeing time is lengthier as compared to other machines.

PH Level different stage of cotton during dyeing period:

STAGE PH VALUE

1 Initial Bath Ph 6.5~7.0.

2. Before Enzyme, bath pH 4.5~4.7

3 After Enzyme pH 5.5~6.0

4 Before Scouring & Bleaching, pH 5.5~5.8.

5 Scouring & Bleaching, bath PH 10.0~10.5.

6 After Scouring & Bleaching, pH 8.5~9.0

7 Before Leveling Chemicals, pH 6.5~7.0.

8 After Leveling Chemicals, pH 6.5~7.0.

9 After Adding Dyes, pH 6.2~6.35.

10 After Addition of Salt, pH 7.5~8.0.

11 After Addition of Soda, pH 10.5~11.0.

12 Before Hot Wash, bath pH 6.8~7.2.

13 Hot Wash, bath pH 8.5~8.7.

14 Before Softener Addition, bath pH 7.2~7.8.

15 After Softener Addition, bath pH 6.5~6.8.

Pretreatment process

Pretreatment is the preparation period of fabric fro dyeing. For getting proper fastness of fabric and proper dyeing pretreatment is a mandatory process. Pretreatment process is occurred by three stages

1. Demineralization 2. Scouring 3. Bleaching

Demineralization: It is a process of removing mineral materials from the water. It is done in water treatment plant. Water from natural sources contains many mineral materials which may hamper the dyeing process. If the mineral materials are present in water then it may lead to uneven shade in dyeing. Besides it may also damage the fabric and the machine.

Scouring: The process to remove fats, oil, waxy substances and added the impurities by certain percentage of alkali treatment and which increase the absorbing power of the textile units, is called scouring.

Bleaching: The process by which the natural color of a fiber can be removed and make the textile this pure white and bright is called Bleaching.

Keya knit composite dyeing section flow chart

Grey fabric receive from knitting section

Batching

Select m/c no

Fabric loading

Select production program

Pre treatment

Select recipe for dyeing

Recipe confirm by D.M/ S.P.O

Dyeing

After treatment

Unload

Water consumption system of Keya knit composite Ltd

M: L = 1:7

Fabric weight =500 Kg

Liquor amount = 3500 - 3700 lit

(1) Scouring:

a. Amount of water : 3500

b. Hot wash : 3500

c. Acid wash : 3500

d. Enzyme wash: 3500

(2) Dyeing:

a. Amount of water : 3400

(3) After treatment:

a. Acid wash : 3600

b. Normal wash : 3700

Total = 24,700

For 1 kg dyed fabric =24700/ 500 = 49.4(near 50) lit water required.

Dyes use in Keya knit composite Ltd

1. Remazol

2. Novacron

3. Anafix

4. Reactobond

5. Synozol

6. Sumifix

7. Dychofix

8. Argazol

Role of chemical bond in dyeing

Chemicals Bonds:  

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole

attraction. The reaction between dyes and fibers must take into account the various types of forces exerted by one molecule upon another.

Covalent Bond:   Bonds resulting in very strong chemical forces that are not easy to break expect under serve conditions are called covalent bonds. The classic example is that of the combination of cellulose fibers with reactive dyestuffs, where the hydroxyl group in the cellulose is covalently bonded to a suitable atom in the reactive dye. 

Vander Waal’s Forces:   These forces are so named because they were first recognized by Van der Waals in 1873. Very weak forces of attraction are always present between the electrons of one atom and the nucleus of another in close enough proximity. Individually these are very weak forces, but collectively they are considered to be of sufficient strength to be the most important attractive forces between dye and fibre. These forces of attraction are known as Van der Waals’ forces. Disperse dyes are held in a polyester fibre by means of Van der Waals’ forces. 

Hydrogen Bonds:   These forces of attraction are weak forces set up between certain atoms in the dyestuff molecule when they are close enough to other atoms in the fiber. One of these atoms is the hydrogen atom, hence the term “hydrogen bond”. Some direct and vat dyes are “hydrogen bonded” in cellulose fibers. 

Hydrophobic Bonding:   The hydrophobic groups, especially alkyl chains, tend to associate together and escape from aqueous environment. The effect due to two simultaneous causes-the Van der Waals’ forces between the hydrogen groups and the hydrogen bonds between water molecules. Each set of forces causes respective assembly of molecules or groups to associate together and to exclude the other. Hydrophobic bonds occur when both the fiber and dye contain a considerable portion of purely hydrocarbon, aliphatic or aromatic, as with some dyes applied on wool or most dyes applied on polyester. It is strictly not a new type of bond or intermolecular force. 

Comparison of the Relative Strength of Dye-Fiber Bonds:

  

Bonds type Relative strength

Van der Waals’ force 1.0

Hydrogen bond 3.0

Ionic bond 7.0

Covalent bond 30.0

Table of Fibers, Dyes and Dye-Fiber Bonds:

  

Fibre Dye class having affinity

Types of dye-fibre bonds

Cellulosic: cotton, jute, rayon, etc.

Direct, vat, solublised vat and sulphur dye

Van der Waals’ forces and hydrogen bonding

Reactive dye Covalent bonds

Protein/polyamide: wool, silk, nylons

Direct, acid, metal complex and basic dye

Ionic bond or electrostatic bonds

Reactive dye Covalent bonds

Polyester Disperse dye Van der Waals’ forces and hydrogen bonding

Acrylic Cationic Ionic bond or electrostatic bonds

Disperse dye Van der Waals’ forces and Hydrogen Bonding.

Keya knit composite Knit Dyeing process with Reactive Dyes

Recipe:

1. Anti creasing agent = 0.3g/L2. Sequestering agent = 0.5 g/L3. Leveling agent = 0.8g/L

4. Glauber salt or NaCl =80 g/L5. Dye (reactive) = x%6. Soda ash =5g/L7. Or caustic soda =1 g/L8. Acetic acid = 0.75 g/L9. Soap = 0.25 g/L10. M: L = 1:711. Time =`120 min12. Temperature = 90-95C

Function of these Ingredients:

 Anti creasing agent is used to remove crease mark from fabric.  Sequestering agent is used to convert hard water into soft water.  Gluber salt is used for exhaustion of dye in the fiber.  Soda ash and caustic soda are used for fixation of dye in the fiber.  Acetic acid is used for neutralizing the dyed fabric.  Soap is used for washing the dyed fiber.

Dyeing Curve:

Dyeing Curve

Dyeing Procedure: 

At first fabric, required water and required anti creasing agent is added in the dye bath. Then sequestering agent and gluber salt of required amount is added in the dye bath. Then the bath is kept rest for 5 minutes. After that reactive dye of required amount is added in the dye bath. After adding dye in the dye bath, the bath is kept for 30 minutes. During this period exhaustion of dye

occurs in the fabric. Then required amount of alkali is added for fixation of dye into the fabric. After adding alkali we will wait for 50 minutes and then we will check the shade. If shade is all right then fabric will be taken for after treatment. 

After Treatment of Reactive Dye:

1) At first dyed fabric will be treated with hot water at 130C for 10 minutes. 2) Then the fabric will be treated with stock solution of acetic acid for 10 minutes at 120Cfor neutralizing the fabric. 3) Then the fabric is washing with soap solution for 15 minutes at 95C. 

Dyeing Process Flow Chart for 100% Cotton Knit Fabric (Turquoise Color)

Turquoise Color:

Turquoise is the color of the gem turquoise. It is a slightly greenish shade of cyan. Turquoise is sometimes described as a mixture of pale blue and green. The name comes from the French for Turkish.

Turquoise Color

Types of Turquoise Color:  There are six type of Turquoise Color. They are given below: 

1. Pale Turquoise (web color) (Hex: #AFEEEE) (RGB: 175, 238, 238)2. Turquoise Blue (Hex: #00FFEF) (RGB: 0, 255, 239)3. Bright Turquoise (Hex: #08E8DE) (RGB: 8, 232, 222)4. TURQUOISE (web color) (Hex: #40E0D0) (RGB: 64, 224, 208)5. Medium Turquoise (web color) (Hex: #48D1CC) (RGB: 72, 209, 204)6. Deep Turquoise (web color Dark Turquoise) (Hex: #00CED1) (RGB: 0, 206, 209)

Process Flow Chart for 100% Cotton Knit Fabric (Turquoise Color):

Turquoise is very sensitive color. Its wash fastness is not good. Dyeing process of turquoise color is slightly difference from other color process.

 

Process Sequence of Turquoise Color:  Fabric loaded 

↓

Treating with anti-creasing agent (Room temperature) 

↓

Adding detergent 

↓

Adding Antifoaming agent 

↓

Caustic dosing (dosing 6min) 

↓

Peroxide dosing (60˚c; 5min) 

↓

Run time 1 hour 95˚c 

↓

Sample check 

↓

If ok 

↓

Drain out 

↓

Normal hot (70˚c, 10min) 

↓

Drain 

↓

Adding Peroxide Killer 

↓

Run time 55˚c, 10min 

↓

Adding Acetic Acid 

↓

Run time 10min 55˚c (ph-4.5) 

↓

Adding enzyme 

↓

Run time 1hour, 55˚c 

↓

Enzyme hot- 70˚c, 10min 

↓

Drain 

↓

Filling in the tank (run time 5min) 

↓

Rinsing -4min 

↓

Drain 

↓

Filling in the tank 

↓

Adding Leveling, Antifoaming & Anti-creasing agent (R.T.) 

↓

10min run time (R.T.) 

↓

10min run time (60˚c) 

↓

Color dosing-30min 

↓

10min run 

↓

½ Salt dosing-5min 

↓

½ Salt dosing -5min 

↓

Runtime -25min (60˚c) 

↓

Sample check 

↓

Soda dosing (2 g/l; 20min) 

↓

Remaining Soda dosing (30min) 

↓

20 min run 

↓

Temp rise 80˚c 

↓

Run time-1 hour 

↓

Rinsing-5min 

↓

Drain 

↓

Filling in the tank 

↓

Run time (RT) 

↓

Drain 

↓

Filling in the tank 

↓

Normal hot (60˚c, 10min) 

↓

Sample check 

↓

Drain 

↓

Adding Acetic Acid (room temp, run time-30min) 

↓

Sample check 

↓

Drain 

↓

Filling in the tank 

↓

Adding soaping agent (90˚c, run-10 min) 

↓

Drain 

↓

Sample check 

↓

Filling in the tank 

↓

Rinsing (5min room tem) 

↓

Drain 

↓

Filling in the tank 

↓

Run time (5min, room tem) 

↓

Drain 

↓

Filling in the tank 

↓

Dosing-fixing agent (15min) 

↓

Run time (20min, room tem) 

↓

Sample check 

↓

Drain 

↓

Filling in the tank 

↓

Dosing softener (5min) 

↓

Run time (20min, room tem) 

↓

Sample check 

↓

Unload

Colour Measurement The color of textile dyes is measured using the spectrophotometer. There are different spectrophotometers for different types of light e.g. Infrared spectrometer, ultraviolet- visible spectrophotometer etc. but the working principle is almost the same. 

Fig : color measurement system of spectrophotometer.

Keya knit composite Ltd yarn dyeing

Yarn Dyeing: Yarn dyeing is slightly difference from woven or knit dyeing. Dyed yarns are used for making stripe knit or woven fabrics or solid dyed yarn fabric or in sweater manufacturing. Yarns are dyed in package form or hank form by yarn dyeing process.  Dyeing process can be vary depending on the individual procedure of a textile engineer or a dyeing master. Now I will give typical flow chart of yarn dyeing. 

Process flow chart for 100% Cotton Yarn (Dark/Medium/Light shade):

Pretreatment

Batch loaded ↓

Demineralization (50˚C, 20 min; PH=4.5) ↓

Scouring & bleaching (100˚C×40 min.) ↓

Drain ↓

Rinse ↓

Drain ↓

Neutralization with acid (50°C ×20 min) ↓

Hot Wash with peroxide killer (60˚C,20 min.) ↓

Drain 

 

Dyeing↓

Leveling agent & Salt (60° × 20 min; PH=6) ↓

Color dosing (60°C×20 min.) ↓

Run time = 10 min. (60°C) ↓

Color migration (80°C × 20 min.) ↓

Cooling (60°C) ↓

Level Check ↓

Soda dosing (60°C×30 min.) ↓

Dyeing run (Dark-60°C×60 min;Medium-60°C×40 min;Light-60°C× 30 min) 

↓Dyeing sample check 

↓(If Ok) 

↓Drain 

 

After-treatment↓

Rinse (with cold Water) ↓

Neutralization after dyeing (50°C×20 min.) ↓

Drain ↓

Soaping (Hot wash) ↓

Drain ↓

Rinse ↓

Add finishing chemical(60°C×20 min) ↓

Drain ↓

Unload

Soft winding:

The precision winders are used to transfer the yarn from paper cones to specially designed shells (bobbins). The process of transferring yarn from paper cones to shells is called soft winding. The soft winding by the precision winders can heavily affect the final result of dyed yarn; therefore, imported precision winders are preferable instead of locally manufactured machinery. Package quality always influences the processes that come prior to or after the dying process. The proper density and homogeneity of the package allows the color to penetrate between the various layers of yarn, producing a uniform flow inside the batch.