Direct dye have higest substantivity towards fibers. it can be directly applied to textile materials due to its highest substantivity towards fiber. So, this dye is called direct dye.
direct dye is also work as a salt ‘colours’ because common salt Or glauber’s salt is used. it is also know as substantive dye.
It is use for dyeing of cellulose fibers as well as proteins fibers such as wool and silk. It required after treatment for improving depth of shade.
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• It is called direct dye because it can be directly applied to the textile material due to its higest substantivity towards fibre.
• Direct dye is also know as “salt colours ” because common salt or Glauber’s salt is used. it is also know as substantive dye.
• Direct dye is highly soluble in water. so dye is easily dissolve in water and dyeing process is carried out at alkaline condition.
• Direct dye is mostly used for cellulosic materials because this dye have good affinity for cellulosic materials compare with other materials. proteins fibres can also be dyed with direct dye.
• direct dyeing process is simple and cheap. and in case of direct dyeing, it required after treatment for improving shade of dyed materials.
• This dye have ability to dyed proteins fibre such as wool, silk and nylon.
• this dye required electrolyte for proper exhaustion. Maximum exhaustion is at 80°C. this is the basic reason it produces proper shade on cellulosic materials.
• dye will direct apply on cellulosic materials such as cotton in alkaline bath and its produce good shade on cotton without any after treatment but washing fastness properties is not proper.
• It required after treatment then it is easily improve washing fastness properties of cellulose materials.
• direct dyes is anonic types dyes and mostly its used for cellulosic materials and proteins fibres also such as Wool, silk, nylon but in case of protest fibre after treatment is required for proper shade.
Properties of direct dye
• direct dye have good solubility in water.
• Electrolyte is required for proper exhaustion.
• This dye is more useful for cellulosic materials such as cotton as well as proteins fibres such as wool, silk, and nylon.
• direct dyeing process is not produce proper fastness properties so generally after treatment is required for shade development.
• Dyed materials are treated with formaldehyde for improving depth of shade.
Formaldehyde (40%) -. 2-3 % owf
Acetic acid (30%) – 1% owf
Treatment is acrried out at 60°- 70°C for 30 mint then rinse and dried.
• fastness property is poor.
• direct dyeing process is comparatively cheap compared with reactive dye and also vat dye.
• direct dyeing process is also be used for dyeing of low grade materials.
• direct dye have good affinity for cellulosic materials and as well as proteins fibres.
• direct dyeing process is carried out in alkaline bath.
• uses Nature of direct dye is anionic.
• direct dyeing process is done at low temp
• This process is very easy to handle.
• direct dye is apply directly on cellulosic materials in alkaline bath then dyeing is done.
• direct dyeing process is not more expensive compared with Reactive dye process.
• after treatment is required for improvement overall shades.
Classification Of Direct Dyes
direct dyes is classified with three steps.
Steps – 1
• Self leveling dyes.
Step – 2
• self controllable dyes.
Step – 3
• Temp controllable dyes.
Self leveling dyes
• This dyes have good migration properties.
• starting stage of dyeing may be uneven dyeing occurs but this dyes is required long time for even dyeing.
• Not required salt for exhaustion.
Self controllable dyes
• This dyes have not good migration property.
• required salt for even dyeing.
• time taken or it is very difficult for even dyeing.
Temp controllable dye
• This dyes have poor levelling properties.
• required salt for proper exhaustion.
• This dye have ability to maintain exhaustion with the help of temperature.
• In this case proper or even dyeing is possible.
Direct Dye Mechanism
The main mechanism of direct dye is when the cellulose materials is immersed in dye bath solutions of direct dye then some important mechanism will occur such as,
1. Swelling (start swelling)
2. Adsorption ( easy adsorption)
3. Diffusion (diffuse dye molecule)
Direct dye have good affinity for cellulosic materials such as cotton. This is the reason when cotton material is inter in dye bath then first of all fabric start swelling and then adsorption and then diffusion will take place during dyeing.
The affinity of direct dye is also contacted with conjugated bonds and Vander wall’s forces. This are very helpful for dyeing.
Direct Dye Recipe
Mainly this recipe is used for cellulose materials in textile dyeing industry.
• direct dye – X%
• wetting agent – 1- 2 g/l
• levelling agent – 0.5 – 1 g/l
• sequestering agent – 1- 2 g/l
• lubricant – 1- 3 g/l
• soda ash – 1- 5 g/l (depand upon light shade/ deep shade)
• Glauber salt – 5 – 20 g/l
• Temp – 95 °C
• Time – 30- 35 mint
• pH – alkaline condition
• M:L – 1:5 – 1: 10
Direct dyeing process
Direct dyeing is generally carried out at boiling water to get proper depth of shade for cellulose materials but in case proteins fibres such as wool, silk, and nylon after treatment is required after dyeing for improving depth of shade. In case of direct dyeing some important factor is required for proper depth of shade.Here I m explain about some important factor for direct dyeing.
• first of all dye bath should be proper heated and also focus on how much time is taken for heating dye bath. this is also a important factor for proper dyeing.
• proper maintenance of temp for dye bath.
• dye solubility is also play important roles in direct dyeing.
• Used levelling agent during dyeing because levelling agent is also play important role in direct dyeing.
• Time is also important factor for dyeing. In case of direct dyeing time should be 30 – 50 minutes.
• Step 1 – First of all set the dye bath at 30 – 40°C.
• Step 2 – raise the boiling temperature at 42°C for 60mint.
• Step 3 – After 40 – 45 mint.
• Step 4 – add salt (first stock for light shade)
• Step 5 – add salt 4-5 g/l (second stocks for full depth of shade)
• rins and dry.
Effect of temperature
In case of textile materials dyeing process, the amount of dye is taken for the materials it’s depend upon wright of materials. But for proper dyeing is depand upon temp and the rate of dyeing is also depend upon temp. In case of direct dyeing, dyeing should be start at room temperature and then the temp is raised to the maximum dyeing temperature.
in case of direct dyeing the maximum exhaustion will take place at maximum temperature (60-80°C) but it’s variry dye to dye.
According to this method we get proper depth of shade in case of direct dyeing.
Effect of liquor ratio
• In case direct dyeing, constration of dye in dye bath increase then the dye uptake also be increasing.
• in case of direct dyeing, for proper depth of shade can be obtained by dyeing at low M:L ratio. Because if we used low M:L in case direct dyeing then its produce proper depth of shade. and keep the ratio constant through out the dyeing and also dyeing a lots of materials at same shade. According to this lots of materials can be dyed in textile industry.
After treatment for improving fastness properties of direct dyed materials.
In textile industry, lots of dye fixing agent are used for improving fastness properties. Such as, potassium dichromate, copper sulphate, formaldehyde.
In case of direct dyeing process the percentage of a depth of shade (fastness) is not good. (proteins fibres) so, dye fixing agent is required for improving percentage of fastness or depth of shade.
Here, I m going to explain about some dye fixing agent such as cationic dye fixing agent, potassium dichromate, copper sulphate, formaldehyde etc.
• treatment with cationic dye fixing agent. (For wash fastness properties)
The treatment of dyed materials with 1-2% of cationic dye fixing agent is carried out for 1/2 hours then rinsing and drying.
treatment with copper sulphate ( for light fastness properties)
The treatment of dyed materials with
copper sulphate – 0.5 – 2%
Acitic acid – 0.5 – 2%
is carried out at 80°C for 30-45 mints. and the materials is the rinsing and drying.
treatment with potassium dichromate
Potassium dichromate – 2 – 3%
Acetic acid – 2 – 5%
Treatment is carried out at boiling the materials are then rinsing and drying.
treatment with formaldehyde
Treatment of dyed materials with
Formaldehyde – 2 – 3% (owf)
Acetic acid – 1% (owf)
Eco-friendly direct dyes
1. In case of eco-friendly direct dyeing process, first, do not use banned azo dyes which liberate harmful amines.
2. You can use optimized solubilizing group in chromophore to give blance between solubility and substantivity.
3. Dont use exhaust method you can use padding method.
4. Properly recycling of dye bath.
5. Recovery of salt by reverse Osmosis.
Preparation of disazo direct dye
direct dye preparation is done by following steps,
Cango red : it is prepared by coupling two molecules of Naphthionic acid with benzidine.
Advantages and Disadvantages of Direct Dye
• Cheap process.
• Easy to handle.
• This dyes are more suitable for cellulosic materials.
• simple process.
• Wash fastness is low.
• This dye have low light fastness.
• This dyes are dull in colour.
• This dye have not capability to dyed for synthetic materials such as polyester fabric.
Uses Of Direct Dye
• direct dye having capability to dyed the all cellulosic materials such as cotton.
• some time this dye is also be used for proteins fibres such as wool, silk etc.
• This dye is gives good accuracy of depth of shade at low temperature. in other word this dye is used at low temperature.
• The main industrial uses of direct dye where wash fastness is not required. because this dye have not good wash fastness properties.
Frequantly asked Question
1. How to prepared of disazo direct dye?
disazo direct dye is prepared by coupling two molecules of Naphthionic acid with benzidine. it is two to three steps reaction. after this reaction cango red 🔴 is formed as a product.
2. What are direct dyes used for?
direct dyes are mainely used for to dye cellulose materials, such as cotton. this dyes is windely used in paper industry.
it is also be used for proteins fibre such as, silk and wool matrials.
it is used for dyeing of paper Or paper related materials. it is also used for dyeing of leather materials.
3. What is Eco-friendly direct dye?
it is not necessary to use any banned azo dyes because it is given harmful amines.
exhaust method is not necessary, you can use padding method.
recycling is necessary for proper depth of shade.
4. What is dyeing process in textiles?
the dyeing process of textile is the interaction between dye and fibre.
In dyeing process of textile process, mainly involved two steps,
Absorption: – transfer dyes from solution into fibre surface.
Diffusion:- dye diffusion is done into fibre Or dye is diffuse into fibre.