Denim Washing,Types of Denim Washing & Process of Denim Washing

Denim Washing:

Denim washing is the aesthetic finish given to the denim fabric to enhance the appeal and to provide strength. 

Dry denim, as opposed to washed denim, is a denim fabric that is not washed after being dyed during its production.

Denim washing

Much of the appeal of dry denim lies in the fact that with time the fabric will fade in a manner similar to that which artificially distressed denim attempts to replicate. With dry denim, however, such fading is affected by the body of the person who wears the jeans and the activities of their daily life. This creates what many feel to be a more natural, unique look than pre-distressed denim.

Types of Denim Washing:
Denim washing are two types. These are

1. Mechanical washes

• Stone wash
• Micro sanding

2. Chemical washes

• Denim bleaching
• Enzyme wash
• Acid wash

Some Important Steps in the Process of Denim Washing: 
1. Pre treatment ( Desizing, Rinsing, Scouring etc) 
2. Enzyme or Stone wash 
3. Clean up to adjust the desire effect 
4. Bleaching 
5. Tinting / Dyeing 
6. Sand Blasting
7. Softening & Much more…..

Vat Dyeing Process / Dyeing Process With Vat Dye

The required water for dyeing is taken in the dye bath and it is maintain at proper temperature (50º- 60 ºC) the reducing and dyeing temperatures vary from dyestuffs to dyestuff. The vatted dye solution may than be added to the dye bath containing the required amount of caustic soda sodium hydro sulphate, kept at recommended temperature.

The well scoured wet yarn is entered in the dye bath and turned several times, so that the affinity of the color may be uniform. The yarn is then kept completely immersed under the dye liquor and the dyeing is continued for one hour. The yarn is turned from time to time… Care should be taken to keep the bath at required temperature and also to keep the yarn thoroughly immersed under the liquor.

The exhaustion agents or retarding agents are added to the dye bath depending upon the dyestuffs taken, during the entire dyeing period. Excess quantities of both sodium hydroxide (NaoH) and sodium hydro sulphate (Na2s2O4) should be present in the dye bath in order to keep the dye in the soluble form. At the end of the dyeing the partly or completely exhausted dye bath must be kept in a distinctly reduced condition; otherwise oxidation of the residual vatted dye takes place in the dye bath itself leading to the appearance of turbidity. This is ensured by adding sufficient sodium hydro sulphate. The dyed goods may then be removed from the dye bath and excess liquor which contains the unexhausted vat dye, sodium hydroxide, sodium hydro sulphate is removed as for as possible from the goods.

The dyed goods are rinsed with cold water and then subjected to an oxidation treatment by exposure to atmospheric oxygen. This is called “air oxidation” or “airing” but the oxidation may be accelerated by using stronger oxidizing agent such as sodium per borate or hydrogen peroxide or sodium dichromate in the presence of acetic acid. This process is usually referred to as chemical oxidation.

During the oxidation step the sodium salt of leuco vat dye absorbed by the fibre is oxidized and converted into insoluble dye in the fibre. At the same time the vatted dye contained in the residual liquor in the goods being dyed also gets converted into the insoluble form which is loosely deposited on the fibre surface. This loosely deposited dye on the surface of the fiber has to be removed for achieving optimum fastness properties especially rubbing and washing fastness properties. This is achieved by soaping process. The dyed material is treated in hot soap solution or a synthetic detergent solution for 15 – 30 minutes. After the soaping treatment the dyed goods should be rinsed thoroughly and finally the dyed material is dried.

Source-Textile learner

DIRECT DYES & ITS DYEING METHOD

Direct Dyes:

Direct Dye is a class of dyestuffs that are applied directly to the substrate in a neutral or alkaline bath. They produce full shades on cotton and linen without mordanting and can also be applied to rayon, silk, and wool. Direct dyes give bright shades but exhibit poor washfastness. Various aftertreatments are used to improve the washfastness of direct dyes, and such dyes are referred to as “aftertreated Direct colors.”Direct Dyes are molecules that adhere to the fabric molecules without help from other chemicals. Direct dyes are defined as anionic dyes with substantivity for cellulosic fibres, normally applied from an aqueous dyebath containing an electrolyte, either sodium chloride (NaCl) or sodium sulfate (Na2SO4)..

The dyeing process with direct dyes is very simple, Direct dyeing is normally carried out in a neutral or slight alkaline dyebath, at or near boiling point , but a separate aftertreatment such as cationic dye fixing , to enhance wet fastness has been necessary for most direct dyeing .

Direct dyes are used on cotton, paper,leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

Chemicals nature of direct dyes:

Chemically they are salts of complex sulfonic acids. 

Structure:-More than 75% of all direct dyes are unmetallised azo structures, great majority of them are disazo or polyazo types.

Ionic Nature:-Their ionic nature is anionic. 

Solubility:-They are soluble in water .

Affinity:-They have an affinity for a wide variety of fibers such as cotton ,viscose, silk jute ,linen etc.. They do not make any permanent chemical bond with the cellulosic fibers but are attached to it via very week hydrogen bonding as well as vander waals forces. Their flat shape and their length enable them to lie along-side cellulose fibers and maximize the Van-der-Waals, dipole and hydrogen bonds. 

Types of direct dyes:

The SDC classification of direct dyes is follows

(1) Class A – dyes that are self-levelling, i.e. dyes of good migration or leveling properties.

(2) Class B – dyes that are not self-levelling, but which can be controlled by addition of salt to give level results; they are described as salt-controllable.

(3) Class C – dyes that are not self-levelling and which are highly sensitive to salt, the exhaustion of these dyes cannot adequately be controlled by addition of salt alone and they require additional control by temperature; they are described as temperature-controllable.

Application of Direct Dyes

Direct dyes are usually applied with the addition of electrolyte at or near the boil in the machines capable of running at atmospheric pressure .But in HTHP dyeing machines it is carried out at temperatures above the boil in case of pure as well as blended yarns. 

An addition of alkali, usually sodium carbonate, may be made with acid-sensitive direct dyes and with hard water as well as to enhance the dye solubilisation. When cellulose is immersed in a solution of a direct dye it absorbs dye from the solution until equilibrium is attained, and at this stage most of the dye is taken up by the fibre. The rate of absorption and equilibrium exhaustion vary from dye to dye. The substantivity of the dye for cellulose is the proportion of the dye absorbed by the fibre compared with that remaining in the dyebath.

Dyeing Method

The color is pasted well and dissolved in boiling water to get a lump free solution .An addition of 0.5–2 g l–1 sodium carbonate may be advantageous when applying dyes of only moderate solubility in full depths.

• The dyebath is set at 40°C,
• Raise to the boil at 2 degC min–1
• Hold at the boil for 30–45 min, 
• During hold add 10–15 g l–1 of sodium chloride or calcined Glauber’s salt. Light shades are dyed without or lesser addition of salt.
• Improved yields can be achieved when applying full depths by cooling to 80°C at the end of the period at the boil, adding a further 5 g l–1 salt and rising to the boil again
• Dye bath variables which must be considered for level dyeing,

1.Temperature of Dyeing and rate of heating

2.Electrolyte concentration and addition

3.Time

4.Dye solubility

5.Use of leveling agent 

After treatment of Direct dyed material

The wet fastness properties (particularly washing, water and perspiration) of virtually all dyeing of direct dyes are inadequate for many end uses but notable improvements can be brought about by after treatments.

• Diazotisation and development 
• Metal salt treatments 
• Cationic fixing agents 
• Formaldehyde treatment 
• Crosslinking agents and resin treatments 

Stripping:- Most direct dyes can be stripped of the use of stripping salts (Sodium Hydrosulphite) and/or by using a chlorine bleaching agent such as sodium hypochlorite, without harmful effects on the fibres.

Color fastness properties of Direct Dyed material:- Generally these dyes are used where high wash fastness is not required.

Wash Fastness:- poor unless treated with suitable dye fixing agent and/or fastness improving finishing agent.

Light Fastness:-Good

Rubbing Fastness:- Moderate to Good

Chemical Wash Fastness:- Poor

Source-Textille Learner

TEXTILE DESIGNS

REACTIVE DYES FOR COTTON

Introduction: 
A dye, which is capable of reacting chemically with a substrate to form a covalent dye substrate linkage, is known as reactive dye.

Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre. This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group of cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group of polyamide or wool fibres.

History: 
Reactive dyes first appeared commercially in 1956, after their invention in1954 by Rattee & Stepheness at the Imperial chemical Industry (ICI). Dyestuffs Divion site in Bleckley, Manchetor. UK.

Usages: 

By reactive dyes the following fibres can be dyed successfully:
1) Cotton, rayon, flax and other cellulosic fibres.
2) Polyamide and wool fibres.
3) Silk and acetate fibres.

Trade names:

Trade name	Manufacturer	Country
Munnactive	Munna Dyechem	India
Ciba cron	Ciba	Switzerland
Remazol	Hoechst	Germany
Levafix	Bayer	Germany
Reactone	Geigy	Switzerland
Primazin	BASF	Germany
Drimarine	Sandoz	Switzerland

Properties of reactive dye: 

1) Reactive dyes are cationic dyes, which are used for dyeing cellulose, protein and polyamide fibres.
2) Reactive dyes are found in power, liquid and print paste form.
3) During dyeing the reactive group of this dye forms covalent bond with fibre polymer and becomes an integral parts of the fibre.
4) Reactive dyes are soluble in water.
5) They have very good light fastness with rating about 6. The dyes have very stable electron arrangement and can protect the degrading effect of ultra-violet ray.
6) Textile materials dyed with reactive dyes have very good wash fastness with rating Reactive dye gives brighter shades and has moderate rubbing fastness.
7) Dyeing method of reactive dyes is easy. It requires less time and low temperature for dyeing.
8) Reactive dyes are comparatively cheap
9) Reactive dyes have good perspiration fastness with rating 4-5.
10) Reactive dyes have good perspiration fastness.

General structure of reactive dyes: 

The general structure of reactive dye is: D-B-G-X.

Chemical structure of reactive dyes

Chemical structure of reactive dyes

Here,

D= dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse, premetallised dye etc.
B = bridging part.
Bridging part may be –NH- group or –NR- group.
G = reactive group bearing part.
X= reactive group.

Classification of reactive dyes: 

Reactive dyes may be classified in various ways as below:

1) On the basis of reactive group: 
a) Halogen (commonly chlorine) derivatives of nitrogen containing heterocycle, like 3 types-
· Triazine group
· Pyridimine group
· Quinoxaline dyes
Example: 
Triazine derivatives: procion, cibacron.
Pyridimine derivatives: reactone
Quinoxaline derivatives: levafix.

b) Activated vinyl compound: 
· Vinyl sulphone
· Vinyl acrylamide
· Vinyl sulphonamide.
Example: 
Vinyl sulphone: Munnactive
Vinyl acrylamide: primazine
Vinyl sulphonamide: levafix.

2) On the basis of reactivity: 
a) Lower reactive dye: Medium reactive dye: here pH is maintained 11-12 by using Na2CO3 in dye bath.
b) Higher reactive dye: here pH is maintained 10-11 by using NaHCO3 in dye bath.

3) On the basis of dyeing temperature:

a) Cold brand: 
These types of dyes contain reactive group of high reactivity. So dyeing can be done in lower temperature i.e. 320-600C.
For example: MUNNACTIVE M, LIVAFIX E.

b) Medium brand: 
This type of dyes contains reactive groups of moderate reactivity. So dyeing is done in higher temperature than that of cold brand dyes i.e. in between 600-710C temperatures.
For example, Munnactive, Livafix are medium brand dyes.

c) Hot brand: 
This type of dye contains reactive groups of least reactivity. So high temperature is required for dyeing i.e. 720-930 C temperature is required for dyeing.
For example MUNNACTIVE H, CIBACRON are hot brand dyes.

Dyeing mechanism of reactive dye: 

The dyeing mechanism of material with reactive dye takes place in 3 stages:-

1. Exhaustion of dye in presence of electrolyte or dye absorption.
2. Fixation under the influence of alkali.
3. wash-off the unfixed dye from material surface.

Now they are mentioned below:

Dye absorption: 
When fibre is immersed in dye liquor, an electrolyte is added to assist the exhaustion of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize absorption. So when the textile material is introduces to dye liquor the dye is exhausted on to the fibre.

Fixation: 
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-NH2 group of fibre and thus forming strong covalent bond with the fibre and thus forming strong covalent bond with the fibre. This is an important phase, which is controlled by maintaining proper pH by adding alkali. The alkali used for this create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place in this stage is shown below: -

1. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Cell   =  D-SO₂-CH₂-CH₂-O-Cell + NaHSO₃

2. D-SO₂-CH₂-CH₂-OSO₃Na + OH-Wool   =   D-SO₂-CH₂-CH₂-O-Wool + NaHSO₃

3. Wash-off: 

As the dyeing is completed, a good wash must be applied to the material to remove extra and unfixed dyes from material surface. This is necessary for level dyeing and good wash-fastness. It is done by a series of hot wash, cold wash and soap solution wash.

Application method: 

These are 3 application procedures available:
1. Discontinuous method-

-Conventional method
-Exhaust or constant temperature method
-High temperature method
-Hot critical method.

2. Cotinuous method-

-Pad-steam method
-Pad dry method
- Pad thermofix method

3. Semi continuous method-

- Pad roll method
- Pad jig method
- Pad batch method.

Stripping of reactive dye: 

The reactive dye cannot be satisfactory stripped from fibre due to covalent bond between dye molecule and fibre. Stripping becomes necessary when uneven dyeing occurs.

Partial stripping: 
Partial stripping is obtained by treating the dyed fabric with dilute acetic acid or formic acid. Here temperature is raised to 70-100°C and treatment is continued until shade is product of hydrolysis. The amount of acid used is as below: -

Glacial acetic acid : 5-10 parts
With water :1000 parts
Or
Formic acid :2.5 to 10 parts
With water :1000 parts
Temperature : 70 - 100°C
Time : until desired shade is obtained.

Different methods of reactive dye application: 

1) Pad-batch method.
Pad batch processes are of two types-

a) Pad (alkali)-batch (cold) process.
b) Pad (alkali)-batch (warm or hot) process.

2) Pad dry method
3) Pad steam method.

Conclusion: By this experiment we came to know the reactive dyes are of the least reactivity because they take more temperature and more time for dyeing.

Dyeing & The General Idea For It

Dyeing is a distribution process in which the dye or pigment is distributed at least two phases or phase systems i.e; the dye/pigment bath or solution and the textile material. Dyes / pigments are generally coloring materials for dyeing operation. There are various types of dyes and pigments for the coloration of Textiles.

General Idea about dyeing: 

1. Textile Materials : Fiber, Yarns and Fabrics are the Textile raw materials for dyeing. These are the products which are dyed by a color or dye. So the first component for dyeing is the raw materials.

2. Dyes or Pigments: Dyes and pigments are one of the important object for dyeing purpose. Without it nothing can be colored and dyed. Because its the main source of color.

3. Chemicals and Auxiliaries : There are some chemicals need for dyeing operation. They are used for increasing strength, stability, performance, etc.

4. Utilities : Coloration can not be done by only with Materials and dyes, it needs some utilities too. These are the main producer of dyeing or coloring materials. Water, Gas, Electricity etc. are the main source of a production. So without the help of Utilities production cant be done.

5. Dyeing Machine : Without machine no operation can done.

6. Machine for After treatments: For better performance and better look machine of after treatments is used.

History of Indigo Dyes

Background

Indigo, or indigotin, is a dyestuff originally extracted from the varieties of the indigo and woad plants. Indigo was known throughout the ancient world for its ability to color fabrics a deep blue. Egyptian artifacts suggest that indigo was employed as early as 1600 B.C. and it has been found in Africa, India, Indonesia, and China.

The dye imparts a brilliant blue hue to fabric. In the dyeing process, cotton and linen threads are usually soaked and dried 15-20 times. By comparison, silk threads must be dyed over 40 times. After dyeing, the yarn may be sun dried to deepen the color. Indigo is unique in its ability to impart surface color while only partially penetrating fibers. When yarn dyed with indigo is untwisted, it can be seen that the inner layers remain uncolored. The dye also fades to give a characteristic worn look and for this reason it is commonly used to color denim. Originally extracted from plants, today indigo is synthetically produced on an industrial scale. It is most commonly sold as either a 100% powder or as a 20% solution. 

History

The name indigo comes from the Roman term indicum, which means a product of India. This is somewhat of a misnomer since the plant is grown in many areas of the world, including Asia, Java, Japan, and Central America. Another ancient term for the dye is nil from which the Arabic term for blue, al-nil, is derived. The English word aniline comes from the same source.
The dye can be extracted from several plants, but historically the indigo plant was the most commonly used because it is was more widely available. It belongs to the legume family and over three hundred species have been identified. Indigo tinctoria and I. suifruticosa are the most common. In ancient times, indigo was a precious commodity because plant leaves contain only about small amount of the dye (about 2-4%). Therefore, a large number of plants are required to produce a significant quantity of dye. Indigo plantations were founded in many parts of the world to ensure a controlled supply.