Introduction to Napthols

are azoic dyes which are largely used in handloom sector to dye cellulosic fibers. They are termed as such because their molecules hold an azo group. Distinguished by their brightness, magnificence and overall fastness features, they help to create some of the vividly colored fabrics. Some of the shades regularly produced by dyers include orange, brown, yellow, scarlet, golden yellow, black, red, violet etc.

What Is the Dyeing Procedure of Napthol Dyes

Napthols are best suited for cellulosic and man made fibers though they are used on acetate and nylon in special cases. The application technique of these dyes is quite like that of developed dyes due to the involvement of diazotizing. The method of application is a two-step process with the first step comprising immersion of the fabric in napthol solution. This is done so as to permeate the fibers. The next step includes immersion of fabric into the diazotized color bath.

The napthol solution is prepared by dissolving napthol in water with the aid of sodium hydroxide and this is used for permeation into the fibers. If the fabric in question is cotton then this process can be carried out under room temperature otherwise a temperature ranging from 80 to 85 degree C is required for viscose rayon. The material is wrung out for ensuring removal of surplus solution if any before going into the second stage of the process.

The second stage of the process involves passing the fabric through diazonium ion solution which is termed as coupling. Normally, diazotization is carried out in vessels made of plastic, wood, stainless steel or earth ware. It is essential that vessels made of zinc, copper and iron are avoided at any cost. Another factor to be ensures is that a major part of the dye formation takes place within the fiber's polymer system at every step of the dyeing process. Several chemicals play an important role in

Fastness Attributes of Azoic Dyes

Azoic dyes have very good attributes with regard to fastness. It has vastly superior light fastness and would need continuous UV exposure if any adverse impact has to be seen on fabrics dyed with azoic dyes. They also have high wash fastness feature and hence they are not affected during laundering. They may however, experience low rub-fastness though this can be controlled through neutralization. This means that it has to undergo soaping off at every step of dyeing. Sometimes, a matt effect may be caused by azoic dyes more commonly on viscose rayon. All azoic dyes are distinctive due to their vibrant orange and red colors.

Precautions to be undertaken in Napthol Dyeing

Fabric has to be safeguarded from water spotting, chlorine fumes, steam acid and UV exposure after application of napthol. Excess salt usage in napthol bath has to be avoided at all costs. Temperature plays a crucial role in base formulation stem as that can otherwise obstruct diazotization. Immediate rinsing of the fabric is essential after developing as otherwise that can damage the fabric. Alkali binding substances have to be used adequately in order to prevent precipitation of developing bath.

On a Concluding Note

Napthols are just one of the several colorant types available in the market today. Each colorant has a distinct advantage and their use will be determined depending upon your requirements.