Types of Textile Dyes, Dyes Used in Textile Industry

Dyes Used in Textile Industry

Textile Dyes

Dyes are colored organic compounds that impart color to various substrates including paper, leather, fur, hair, drugs, cosmetics and waxes, and textile materials. Dyes are normally used in solution, which is capable of being fixed to a fabric.

According to the Application Form Classification of Dyes:

1. Ready-made Dyes

A.Water Soluble Dyes

• Direct (Cotton)
• Acid (Wool, Silk)
• Basic (Jute, Acrylic)
• Reactive 

B. Water Insoluble Dyes

• Vat (Denim)
• Sulphur (Umbrella Cloth)
• Disperse (Polyester)

2. Ingrain Dyes

• Azoic 
• Oxidation Color
• Mineral Color

Suitability of Various Dye-Classes for Textile Fibers:

• Cellulosic (Cotton/viscose) - Direct, reactive, vat, sulfur, oxidative, azoic, etc.
•  Cellulosic (Jute) - Basic dyes are widely used.
• Protein (Wool, Silk, Nylon) - Acid dyes are mainly used
• Polyester, cellulose, acetate - disperse dyes are mainly used

Ways of Coloration:

• Direct dyeing, in which the dye from the solution in contact with the textile material is gradually absorbed due to affinity.
• Dyeing with a soluble precursor of the dye, which forms an insoluble pigment deep within the fibers on treatment
• Dyeing is followed by a chemical reaction of the dye with appropriate groups in the fiber.
• Adhesion of pigment to the fiber surface of the fibers by using appropriate binder.

Direct Dyes

Direct dyes are also known as substantive dyes because they are strongly substantive to cellulosic fibers. Direct dyes have inherent substantivity for cotton and other cellulosic fibers.

Properties of Direct Dyes:

• Direct dyes are capable of dyeing cellulose, protein, and polyamide fiber without preliminary mordanting. However, widely applied in cotton.
• Available in a full range of hues but do not have color brilliance.
• The liquor of direct dyes is complex
• The solubility of the dye greatly depends on the chemical structure.
• Solubility increases considerably with liquor temperature
• A considerable member of direct dyes forms precipitates with Mg and Ca salts.
• Direct dyes have poor wash fastness but can be increased by various after treatment on the fiber
• Light fastness on cellulosic fiber varies from poor to fairly good but some copper complex dyes have good light fastness
• They provide a wide range of hues

Commercial Name of Direct Dyes

• Chlorantine fast -Ciba
• Sirius, Sirius Light - Bayer
• Pontamine - Du Pont
• Durazol, Chlorazol, Gcyl - ICI
• Diphynyl, Polyphenyl, Solorphenyl - Grigy

Effect of Different Variables:

• Effect of Electrolytes: The addition of electrolytes to the dye liquor tends to promote exhaustion of direct dyes. Cellulose fibers assume a negative charge when immersed in water. This has the effect of repelling the similarly charged ion of the dye. Electrolytes reduce the charge on the surface of the fiber, thus facilitating the approach of the dye ion which makes hydrogen and vanderwalls force effective.
• Effect of Temperature: An increase in temperature decreases the amount of dye absorbed by the fiber at equilibrium, by increasing the kinetic energy it does.
• Effect of pH Value: Direct dyes are almost invariably applied from a neutral solution. The addition of acid may cause alter the shade. Mild alkali has a retarding effect on the rate of absorption.
• Fastness: Direct dyes do not have good fastness properties to washing or other wet processes. Some of the direct dyes have moderate light fastness, and the rest of them are quite good.

Acid Dyes: 

Most of the acid dyes are sulphonic acid salts, but a few contain a carboxyl group. 

Acid dyes are called firstly because the original members of these classes were applied in a bath containing the mineral or organic acid and secondly, because they were nearly sodium salts of organic acid.

How is Protein Fiber Attached to Acid Dyes?

The acid used in the bath ranges from sulphuric acid (pH<2) to aluminum acetate (pH>6.5) Since they are anionic in an aqueous solution, they will dye fiber with cationic sites. The fiber absorbs acids. The acid promotes the fiber amino group, so it becomes cationic.

Dyeing involves the exchange of the anion associated with an ammonium ion in the fiber with a dye anion in the bath. 

Fiber- NH2 +  H+ (aq) + HSO4-(aq)  =   Fibre- NH3+SO4H-

Fibre- NH3+SO4H- + Dye- SO3-  =  Fiber-NH3+SO3-Dye

Effect of Different Variables of Acid Dyes:

Effect of Salt: The added glauber's salt act as a retarding and leveling agent sulfate, bi-sulfate, or chloride ions inhibiting the initial strike of the dye and blocking the ammonium salt in the wool. 

NH2 - W/P - COOH + Na2+SO4-  =  NH3+SO4- -W/P - COOH

Effect of Acid: Most of the acid dyes will not exhaust on wool at all unless the dyestuff has been acidified. Different acids provide different shades because of their reactivity. 

Effect of Temperature: The rate of absorption of acid dyes is greatly influenced by temperature. Temperature increases the rate of absorption, but each dye has its own temperature which gives maximum output.

Classification of Acid Dyes: 

According to characteristics acid dyes can be classified into four types:

• Levelling dyes
• Fast acid dyes
• Milling dyes
• Super milling acid dyes

Basic Dyes

Basic dyes have free basic amino groups which are capable of reacting with acid dyes, therefore basic dyes are called Basic dyes.

Properties of Basic Dyes:

• The outstanding characteristics are the intensity and brilliance of the color 
• Readily soluble in alcohol or methylated spirit
• Not easily dissolved in water
• Some of them are decompose by boiling water
• When treated with water it decomposes
• Basic dyes in certain conditions can be precipitated by direct dyes
•  Poor light fastness and poor to moderate wash fastness
• Hard water should not be used with basic dyes

Nature of Affinity of Basic Dyes: 

Cellulose fiber have no affinity for basic dyes. A few days have little affinity for cotton, but their wet fastness is not good. In the case of protein fiber, the affinity of basic dyes is of chemical nature. The reaction is one kind of salt formation.

                    W. COO- + (Dye. Cation)+  =  W. COO. Dye.Cation

Dissolving Basic Dyes:

Due to the insolubility and tendency to tar, special precautions are required when dissolving the basic dyes.

The dyestuff is made into a paste with about its own weight of 30 % acetic acid. Sufficient hot water is then added with stirring to dissolve the dye where the temperature must not exceed 60 C

Reactive Dyes

Reactive dyes are so called because it has a reactive group in their molecular structure and that reactive group reacts chemically with fiber polymer molecules and forms a covalent bond. For this reason, the dyes are so-called. It is also known as the fiber reactive group.

Properties of Reactive Group:

• The reactive group of the dye makes the covalent bond with the fiber molecule.
• Water soluble in water
• Normally used for dyeing cellulose and protein fibers.
• All types of shades are available with these dyes
• Dyeing is done in an alkaline condition
• Good wet fastness
• Light fastness and rubbing fastness are comparatively well
• Cheap cost
• The dyeing process is very easy
• Dye reacting group reacts with cellulose OH- group and NH2- group of protein fiber

Vat Dyes

Vat dyes are insoluble color compounds so they cannot be applied directly to the fabric. They have to be converted into their water-soluble forms.

Characteristics of VAT Dyes:

• Excellent wet and light fastness
• Large dyestuff molecules
• Stable against oxidizing
• Not soluble in water
• No brilliant shades are available
• Relatively complicated dyeing method
• Relatively expensive dyestuffs
• Mostly used on cellulose

Why Vat Dyes are So-called?

 The word vat means "vessel". The dye's names are taken from batting. The dyes are kept in wooden vat and make solubilized vat dyes by the process of formal so it is called vat dyes.

Properties of VAT Dyes:

Vat dyes are insoluble in water and cannot be used for dyeing without modification when treated with a reducing agent, they are converted into leuco compounds, which are soluble in water in the presence of alkalies. These leuco compounds are substantive towards cellulosic fibers and re-oxidize to make the insoluble color pigments into the fiber.

Sulphur Dyes

Sulfur dyes are so-called because they contain di-sulfite (S-S) in their chemical structure. The most important class of sulfur dye is sulfur black. In 1893, commercially successful black sulfur was first prepared. It can be applied on cellulosic materials, not to wool or protein fibers due to strong alkaline conditions.

Properties of Sulphur Dyes: 

• Sulfur dyes are cheap and easy to apply
• Good wet fastness
• Moderate light fastness
• A cheap method of dyeing cotton with wet fastness is better than direct dyes
• Poor fastness to chlorine
• Decompose by acid with the liberation of sulfur
• Resembles vat dyes insoluble in water
• Reduce to a soluble form 
• Reverts to the original state of oxidation
• A commonly used reducing agent is Na2S
• Milder than hydrosulfite

Disperse Dyes

Disperse dye is one kind of substance that is free from ionizing groups. Disperse dyes are insoluble or partially soluble in water used for dyeing synthetic textile materials. These dyes derive their name from their insoluble aqueous properties and need for aqueous dispersion by dispersing agents. Disperse dyes are mainly used for polyester yarn of fabric

Properties of Disperse Dyes:

• One kind of organic substance that is free of ionizing group
• Non-soluble in nature
• Insoluble in water
• Dispersing agents are needed for dyeing with dispersed dyes
• Wet and light fastness is good to excellent
• It is mainly used for dyeing synthetic fibers
• Disperse dye dyeing is carried out in high-temperature
• The molecular size of dispersed dye is smaller than other dye
• In some cases carrier method is applied for polyester dyeing

Azoic Dyes 

Normally it is dyed in cold for all natural fibers. Naphthol dyes are not sold in the form of a 'finished dye' but in the form of their components ( Insoluble azo base and fast color coupling compound) Which combine on the fiber to produce a water-insoluble azo dye of excellent fastness properties.

Properties of Azoic Dyes:

• These dyestuffs always contain an azo group in their chemical structure 
• Light fastness properties are admirable
• Shade brightness is also admirable
• Insoluble in water normally
• Dyestuffs are always used in dyeing cellulosic materials.
• The dyeing operation is done by a two-bath arrangement. One is called an impregnation bath and the other is called a developing bath.

Oxidation Color Dye

Oxidation hair dye tends to be the most popular dye on the market today. These products will have the most long-lasting results, given that the dye fully penetrates into the hair. Although the color may fade and new roots will grow the permanent dye will remain in the hair until it is trimmed away. Permanent dyes use chemicals that strip the hair of its natural color and replace it with another color. 

Mineral Color

A naturally occurring inorganic solid that has a crystal structure and a definite chemical composition. More than 3000 identified materials. About 20 materials make up most of the earth's crust.

Properties of Mineral Color

• Color
• Color is the property of minerals that is easiest to identify
• It is also considered an unreliable property to use in identifying the mineral since slight impurities can affect color.
• Color is the perceived wavelength of light that bounces off from the materials and is detected by our eyes