Sunday 28 October 2018

What are Rapid Fast Dyes

The Rapid dyes are stabilized azoic dyestuffs. These are also called as Napthol dyes

 They are applied to the fibers in one operation.

 Bright full colors are obtained with very good fastness properties.

Printing and dyeing with Rapid fast dyes is getting very popular specially in the traditional garments such as sarees. 

Rapid fast dyes is a class of Azoic dyes. These dyes contain an insoluble azo group. These dyes are not found in the readymade form. The dye is produced by a reaction between two components. These components are: 

1. Coupling compound ( Napthol)
2. Di-azo compound or di-azo salt. 

They have excellent wash fastness and light fastness properties, provided these are produced properly.

How the reaction Takes place

1. Naptholisation: Napthols are insoluble in water and they are converted into water soluble compound by treating with alkali. The material is treated with this solution. 

It is important to remove excess napthol from material for improving rubbing fastness. This is done with the help of centrifuging, squeezing or vacuus extraction. 

2. Diazotisation:  A base containing amino group (-NH2) ( which is the dye stuff), reacts with Sodium nitrite to form a solution of diazonium salt by reacting with HCL of H2SO4 in presence of 0 to 50 deg C temperature. Ice is used sometimes for the low temperature, hence they are also called Ice-colors.

3. Coupling: The treated material from the first step is then put in a bath containing diazonium solution to carry out the coupling. Thus the color is produced inside the fabric. The pH is very important here.

The material then is agitated with first water and then boiling water to remove un-reacted color and to enlarge the size of color molecules inside the fiber. 

These are used for producing bright shades of color such as orange, red, scarlet, navy and black.  

These are also used for printing backgrounds so that the foreground becomes prominent. Hence these are suitable where large areas of ground need to be colored. Rapid dyes are mixed with water and boiled with caustic soda and a gum paste. A receipe for rapid dyes is given here.

Certain azo dyes are known to release some aromatic amines which are considered to be carcinogenic. A lot of countries have put ban on these dyes, as discharge of the untreated dyes lead to the toxic pollution of the atmosphere and water. 

Watch this video on how to dye with Azoic dyes in Laboratory

Source: 1 2 3

Thursday 25 October 2018

What is Space Dyeing and What are Space Dyed Fabrics

Space dyeing is a yarn dyeing technique in which a multicolor or blurred dye look is created. It creates a textured pattern and provides more color in the fabric.

Space dyeing can be done in any type of fiber- natural or synthetic. It is normally done on polyester, cotton, rayon, nylon and wool. 

In this method, the yarn is dyed at intervals along its length. There are two methods to produce. In the knit-de-knit method, the yarn is knitted first. Then the knitted cloth is dyed and then it is de-knitted. As dye cannot penetrate the areas where yarn cross, it creates alternate dyed and undyed spaces.

 In the other method, which is also a high speed method, the yarn must be wound on some dye package. It can be Dye Spring, plastic tube or steel tube. The chemicals are color mixtures are mixed and put in the individual color tanks of a space dyeing machine. Dyes are then injected using needles which are inserted into the package.

After dyeing the packages are placed in yarn conditioning machine for fixation and subsequently washed.

The below image gives the process steps

Multiple pattens can be produced as given below


1 2 3 4 5

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