Apparel Dyeing is a process by which color is applied on apparel. Basically through the dyeing process color is applied on fabric. Dyeing is used for giving fashionable look on fabric, and using these fabric, garments manufacture denim, t-shirt, sweater, Shirt, jackets etc.
Objectives of Dyeing
To produce fashionable garments by changing the outlook.
Comparatively low cost
Different shade can be accepted in same batch
Basic Dyeing Process of Garments
Mainly dyeing process is applied on grey fabric and after completing the whole process we get colored fabric. But remember one thing that after Dyeing you have to wash your fabrics.
Flow Chart of Apparel Dyeing
If closely see the flow process of complete Dyeing of fabric, then you may identify the following procedure. Earlier I said that Dyeing process starts with grey fabrics/garments then loading into Dyeing machine, after that pre-treatment and bleaching garments, then Dyeing, fixing (after treatment) and finally we will get finished dyed fabrics.
Bleaching: Bleaching is a chemical process which removes the natural color of Textile fibers. The fiber/yarns/ fabric become permanent white.
Objective of Bleaching
It removes the natural color from textile materials.
It brings the textile materials permanent white.
Improve the absorbency of the textile materials.
Produce textile materials for the next process.
Some fabrics are sold as bleached goods.
A Modern Bleaching Machine
Types of the Bleaching Process
Generally, there are two types of the bleaching process
Hand Bleaching
Machine Bleaching
Hand Bleaching: It is a small scale production process for domestic and cottage industry. Before machine invention, it was practiced until it is in use. It is not a defectless and controlled process.
Machine Bleaching: It is continuous and discontinuous large scale production process. Modern textile industries have used this process. Machine bleaching us controlled and defectless. Production cost is less in the machining process. The bleaching process can be divided into two processes depending on the bleaching agent:
Bleaching by Oxidizing agents
Bleaching by Reducing agents
Oxidizing bleaching agents
Chlorine gas
Bleaching powder {Ca(OCl)Cl
Sodium hypo-chloride (Na2OCl)
Calcium hypo-chloride {Ca(OCl)2}
Potassium di-chromate (K2Cr2O7)
Sodium di-chromate (Na2Cr2)
Potassium permanganate ( KMnO4)
Potassium Chlorate (KClO3)
Sodium peroxide (Na2O2)
Reducing bleaching agents
Hydrogen (H2)
Carbon (C)
Carbon mono oxide
Hydrogen sulfide (H2S)
Sulphur dioxide(SO2)
Ferrous sulphate (FeSO4)
Titenous chloride(TiCl2)
Zinc dust (Zn)
Sodium Sulphate (Na2SO4)
The bleaching agents mentioned above all are not used only the bleaching process. Some bleaching agents are very costly. Some agents cannot bleach completely. Reducing bleaching agents only used for protein fibers.
Hydrogen peroxide can bleach all kinds of fibers. So, it is called universal bleaching agents.
Oxidizing bleaching agents
Oxidizing agents generally are used for cellulosic fibers. If reducing agents are used then after bleaching when fabrics come in contact with air they become yellowish or reddish that is come back to the original color. But oxidizing agents bleach goods free from this defect. So, goods become permanent white. Therefore Oxidizing bleaching agents are generally favored.
Reducing bleaching agents
Protein fibers wool and silk generally bleached with reducing bleaching agents. Because chlorine present in oxidizing agents damages proteins fibers without bleaching action. This is why animal fibers are bleached with reducing agents.
Fiber types choice the bleaching process to be used. Generally, need basis bleaching is made may be half bleach or full bleaching.
Factors considered in the bleaching process
Concentration of chemicals
Liquor ratio (L: R)
pH of the chemical solution.
Time of treatment.
Written by
Engineer Sheikh Nurja
B.Sc engineer of textile
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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 19th 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 and it is getting very popularity because of low cost and availability. On the other hand the natural dye is very much expensive and sourcing of raw materials not easy. Natural dye mainly used in food color but in textile most of the dye are chemical based. You may find that, this chemical based dye is not good for human body.
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 Procedure 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:
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 inserted so that after use remain stable and get long life.
They should have the proper 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
A 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 in Textile
Pigments are used in textile may be broadly classified 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 fibers
Extensive color range with a high light fastness
Disadvantages of Pigment Dyeing and Printing
It has an adverse effect due to binders
Chemical and physical properties of binders influence in dyeing and printing
Using a solvent like kerosene, Spirit, etc. produce the problem of flammability, pollution, etc.
It covers the high cost.
Written By
Engineer Sheikh Nurja
B.Sc engineer of textile
If you like this article please do not forget to share on facebook and put your valuable comments.
Before discussing the classification of dyes lets have some idea of dyes and what can be the basic characteristics of dyes.
What is Dyes
A dye is 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 the most textile dyeing process, the process initially involves the 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 fiber. Depending on the internal structure of the fiber, this occurs down pores, or between fiber polymer molecules. The overall process of adsorption and penetration of the dye into the fiber 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 fiber 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
Written By
Engineer Sheikh Nurja
B.Sc engineer of textile
If you like this article please do not forget to share on facebook and put your valuable comments.
