What is dye

By nahian February 17, 2015 February 26, 2015 Dyeing, Printing

What is dye?

A dye or dye stuff is usually a colored organic compound or mixture that is used for imparting color to a substrate such as cloth, paper, plastic or leather in a reasonably permanent fashion.

In other words, a dyed substrate should be resistance to a normal laundry or cleaning procedures.

Dye can be synthetic or natural i.e. it can be collected from nature or can be made by chemical. Traditionally natural dye was used but in 19^th century synthetic dye produced in a large scale and created demand in the market. Now for dying purpose most of the cases synthetic dye is used rather than natural dyes. Synthetic dye is human made dye getting very popular because of low cost and availability.

White dye

White dye is one kind of commonly used dye. Some colorless compounds are used as the optical brightness. They may also be called white dye. They have the special properties of absorbing uv light & re-emitting the visible light so that the fabric appears bright Example: OBA that means optical brightening agent.

Selection of dye

There are numerous factors involved in the selection of dyes for coloring a fabric in a particular shade. Some of important factors that need to consider before selecting dye are:

Types of fibre
Form of textile materials
Fastness properties
Method of dyeing
Cost
Available machine
Available of dyes.

Written by

Samina Ferdous (pue)

Chittagong textile engineering college (CTEC) 6th batch.

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What is Pigments

By nahian February 17, 2015 February 26, 2015 Dyeing, Printing, Wet Processing

What is Pigments?

Pigments are such colorants which composed of particles that are insoluble in the application medium. They have no substantivity for the material since the particles are too large to penetrate into the substrate. They are generally present on the surface of the substrate. That’s why pigments are made fixed with an adhesive to the surface so that they are not being removed easily.

Pigment Dyed Fabric

A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.

Required Properties of pigments

Pigments should be opaque in such a way that they may have good covering power.
Pigments should be chemically insert so that after use remain stable and get long life.
They should have the properly to freely mix.

General Classification of Pigments

Natural or mineral pigments:

These are pigments such as

Iron
Ores
Clays
Chalk etc.

Chemical or synthetic pigments:

These mainly include

Zinc oxide
White lead
Titanium dioxide
Larger number of inorganic and organic colors

Reactive pigments:

Some pigments on account of their chemical character react with oil, fatty acid and soaps, e.g

Zinc oxide
Red lead

Inert pigment: As for example titanium dioxide

Classification of Pigments as textile use

Pigments are used in textile may be broadly classify as

Azoic pigments
Vat pigments
Miscellaneous pigments

Of all the Azoic pigments are occurring major places in pigments.

Advantages of pigment dyeing and printing

No wet treatment so it is so simple to do dry and curing
It is applicable to all fibres
Extensive color range with high light fastness

Disadvantages of pigment dyeing and printing

It has adverse effect due to binders
Chemical and physical properties of binders influence in dyeing and printing
Using of solvent like kerosene, Spirit etc. produce problem of flammability, pollution etc.
It covers high cost.

Engineer Sheikh Nurja

B.Sc engineer of textile

Merchandiser at buying house

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Classification of Dyes

By nahian February 15, 2015 February 15, 2015 Dyeing, Printing, Wet Processing

Before discussing about the classification of dyes lets have some idea of dyes and what can be the basic characteristics of dyes.

Dyes

A dye is a such type of colorant substance which is capable of imparting it’s color to a given substance, by being soluble in the application medium (usually water) at some points during the coloration process.

Direct Dyes

In most textile dyeing process, the process initially involves transfer of the colored chemical from the aqueous solution onto the fiber surface which called adsorption process. From there the dye slowly diffuses into the fibre. Depending on internal structure of the fibre, this occurs down pores, or between fibre polymer molecules. The overall process of adsorption and penetration of the dye into the fibre is called absorption. Absorption is a reversible process. The dye can therefore return to the aqueous medium from the dyed material during washing which is called desorption.

Major characteristics of dyes

Intense color.
Solubility in water at some point during the dyeing cycle.
Some substantivity for the fibre being dyed.
Reasonable fastness properties of the dyeing produced.

Dyed Finished Fabric

Classification of dyes (according to textile usage)

Acid dyes
Azoic dyes
Basic dyes
Direct dyes
Disperse dyes
Mordant dyes
Pigments
Reactive dyes
Sulpher dyes
Vat dyes