Bifunctional reactive dyes

Bifunctional reactive dyes

Many of the new reactive dyes are bifunctional with identical or different reactive groupings in the dye molecule.Bifunctional dyes carry two reactive groups. They are known for their excellent dyeing efficiency and overall fastness properties. Bifunctional dyes with good dyeing properties are created by the careful selection of the right reactive groups and right chromophores

It can easily be assessed that dyes with two identical reactive groups and dyes with two different  reactive groups exhibit a higher fixation yield than-dyes with one group.

homo and hetero bifunctional dyes
Bifunctional dyes with two similar functional groups are known as homo bifunctional group dyes.
The dyes having two different functional groups are known as hetero bifunctional group dyes.

The dyes were conventional Dichlorotriazine type, with the end condensation of B-sulphato ethyl sulfone to have different type of reactive group in a single molecule. They offer enhanced reproducibility especially for medium to pale shades. Due to triazine ring system, they offer level dyeing performance for even non-critical substrates.

Variables in dyeing with bifunctional dyes
1.Pretreatment of the material
2.Water
3.pH
4.Quality of Electrolyte
5.Alkali system
6.Dyeing temperature and dyeing duration
7.After treatment.

Dyeing method with bifunctional dyes

Method Of Dyeing
Set the dye bath at 20º-30º C and add Glauber's salt, now enter the material.

Run for 20 minutes.

Add half amount of the glauber's salt and continue dyeing.

Now gradually raise the temperature to 60º-65º and dyeing for 15 minutes further

now add soda Ash solution and continue dyeing for 60 minutes.

Wash properly the material.

Washing off procedure for bifunctional dyes

1.Dye bath drain.

2.Intermittent washing in cold

3.Neutralize with acetic acid 

4.Hot wash at 70 Deg C in pressure to remove salt and hydrolysed  dye.

5.Soap at 80-85 deg

6.Hot wash at 90 deg.

7.cold wash.

Dyeing cycle 

Salt & Alkali Requirement for ME Reactive Dyes

Depth of Shade %	Salt g/l (Dye Liquor)	Soda Ash g/l (Dye Liquor)
Up to 0.5	30	10
0.5 to 1.0	35	15
1.0 to 2.0	50	15
2.0 to 4.0	60	20
Above 4.0	80	20

 Advantages of bifunctional dyes
1.They offer enhanced reproducibility especially for medium to pale shades. They have high fixation rate.
2.Due to triazine ring system, they offer level dyeing performance for even non critical substrates. They are less affected by dyeing variables such as temperature , heating rate and alkali dosing.
3.They have high fastness profile especially the washing characteristics.
4.They have a brighter range of colors as compared to VS dyes.
More information on reactive bifunctional dyes
 FAQ about Dyeing and dyes
Multifunctional reactive dyes
Reactive dyeing

Reactive Vinyl Sulfone Dyes

Vinyl Sulphone Based Reactive Dyes

VS dyes are widely used for exhaust dyeing, cold pad batch process and also in automated batch wise dyeing machines. These are also used for printing by one phase or two phase application method. The range offers very good light and wash fastness. Excellent white effect on dyed grounds by discharge and resist printing method. It has high stability in dry state and neutral solution.

Reactive group:- Reactive Dyes are Vinyl Sulphone based Reactive Dyes having Vinyl sulphone as the reactive group.

Reaction with cellulose

They react chemically under suitable conditions with Cellulose based materials in presence of alkali, these dyes react with the hydroxyl group of cellulose and form firm, covalent linkages, yielding brilliant shades with good fastness properties.

Solubility:-

Vinyl Sulphone Base Dyes offer high solubility in water and suitable for both Exhaust/Pad-batch Dyeing and Discharge Printing.

Applicability

VS' dyestuffs posses poor affinity for cellulosic fibers in absence of salt and alkalis. For this reasons, they are suitable for use on pad. Their substantivity can be increased by addition of glauber salt or common salt and alkali, making the dyestuff suitable on all conventional dyeing machine for loose material, yarn in hanks and packages and piece goods.

Dyeing Methods

Due to their versatile nature dyeing methods may therefore, be classified under the padding and exhaust processes, standing baths are not recommended, as in alkaline medium inactivation of the dyestuffs by reaction with water takes place as a side reaction.

These Dyestuffs are unstable under alkaline condition, and therefore water used for their dissolution should be neutral.

Fastness Properties

As the Dyestuffs react chemically with Cellulose based materials, the dyed materials posses good fastness properties.

Dyeing and Dyeing Method

It is possible to use mixture of Vinyl Sulphone Base Dyes for getting combination shades. For this application Vinyl Sulphone Base Dyes of similar properties are to be used.

Dye dissolution:

VS Dyes are dissolved by pasting it with a little water and pouring boiling hot water over it under stirring. The water used should be neutral.

DYEING METHOD :

Conventional method Dyeing Cycle

All in one Method

Isothermal Method

Exhaust Dyeing Method :

1.Take well scoured/bleached material, ensure that pH of the material is below 7.

2.Add predissolved dye and run for 10 min. at 40ºc.

3.Add  Common salt  in 3 instalments at an interval of 10 min. Raise the temp. to 60ºc in 20 min. and run for 20 min.

4.Add alkali (Soda Ash for light medium and dark shades and mixed alkali soda +caustic for extra dark shades)and run for 1 hour.

Salt & Alkali Requirement for VS Based Reactive Dyes

Depth%	Salt Gpl Unmercerized cotton	Salt gpl mercerized cotton	Soda gpl	Fixation time in min.
up to 0.10	5	3	5	30
0.11 - 0.30	10	7	8	30
0.31 - 0.50	20	10	10	45
0.51 - 1.00	30	15	15	45
1.01 - 2.00	40	20	15	45
2.01 - 3.00	50	40	20	60
3.01 - 4.00	60	50	20	60
above 4.00	80	60	Mixed alkali	60-90

After Treatment:-

Rinse cold,

Neutralize with 1-2 cc/lit. Acetic Acid in cold

Soap at 80 -85 C

Repeat the soaping process again for achieving better fastness propertise.

Hot wash,

Cold wash.

Reactive HE Dyeing

High Exhaust Dyes (Reactive 'HE' Dyes)

HE Dyes are Reactive Dyes for cellulosic material and are designed to give high fixation by exhaust dyeing methods when applied at the temperature 75º C - 90º C. HE dyes are suitable for dying cotton and other cellulosic materials. These dyes have significantly higher exhausation and Fixation efficiency which result in appreciable cost reduction, in comparison to Conventional reactive dyes. Some advantages of HE Dyes have:-
(i) Excellent compatibility

(ii) Good built up.

(iii) Excellent Reproducibilit

(iv) Wide Applicability

(v) Outstading built up and consistency.

(vi) Good Overall color fastness properties.

Method Of Dyeing

Set the dye bath at 50º C and add dyestuff. Run for 15 Minutes. Add half of the glauber salt and continue Dyeing Raise the temperature to 80º-85º c and run for 15 minutes. Add soda Ash solution and run 30-60 minutes. Wash properly the material.

Standard Exhaust Methods for HE Reactive Dyes

Salt & Alkali Requirement for HE Reactive Dyes

 

Depth of Shade % Salt g/l (Dye Liquor) Soda Ash g/l (Dye Liquor) Up to 0.5 30 10 0.5 to 1.0 45 15 1.0 to 2.0 60 15 2.0 to 4.0 70 20 Above 4.0 90 20

Soaping After Exhaust Dyeing

(A) Rinse cold water (10-20 min.) Repeat the process until the bath is clear.

(B) Rinse hot to remove electrolyte completely.

(C) Soaping at 85 º C (15-30 min.

(D) Rinse at 90-100 º C (10 min.)

(E) Rinse cold and finish accordingly.

Reactive Dyes

Reactive dyes
In the simplest terms ,all reactive dyes are made up of three basic units, a chormophore , a bridge and a reactive group/ groups (either a haloheteocycle or an activated double bond). These dyes are used for dyeing of cellulosic fibers and when these are applied to a cellulosic fiber in an alkaline dye bath ,they form a covalent bond with hydroxyl group of the fiber by chemically reacting with fiber. The covalent bond formed between the dye molecule and fiber make dye molecule a part of the fiber molecule.


Types of the reactive dyes


Basically there are three types of the reactive dyes , which are classified as per the functional group present,

1.mono functional reactive dyes
2.bi functional reactive dyes(homo and hetero bifunctional)

3.poly functional or multifunctional reactive dyes

These dyes are also classified based on their exhaustion properties as well as on their application temperature such as cold brand  and hot brand reactive dyes.

These are water soluble dyes and hence applied from aqueous  bath under neutral to weakly acidic conditions , electrolyte is added to exhaust the dyes on the fiber from the dye bath and then  exhausted dye is fixed on the fiber by adjusting the pH suitable for making a covalent bond between the dye molecule and fiber , with the help of alkali. The unexhausted dye which remains in the liquor is hydrolysed ( hydrolysed dye is formed by the reaction of dye molecule with water under alkaline conditions) and loses its reactivity with cellulosic fiber , that too is absorbed by the fiber . Therefore washing and soaping treatment is done to remove the hydrolysed and excess dye to improve the color fastness of the dyed substrate. The overall colorfastness achieved is good when the material is dyed and washed properly.

Dyeing cycle and Important factors/phases  in reactive dyeing

1. pretreatment of the substrate
2. pH of the substrate prior to dyeing
3. pH of the dyebath
4. solubility of the dyestuff
5. dyeing temperature
6. electrolyte concentarion
7. dyeing time
8. M:L
9. Type of alkali
10. Washing off sequence
11. Quality of water and salt

The  detail of impact of above parameters,

1. Pretreatment of the substrate

The process of removing natural impurities like oils, fats, waxes, pectin, protein, amino acids and hydrophobic impurities from a yarn or fabric is called “Scouring”. Scouring is done to improve absorbency of the textile material by removing the oils and fat in the yarn or fabric by boiling.

The pretreatment includes the scouring and bleaching of the substrate prior to dyeing . The main objective of the scouring treatment is remove the major impurities from the cotton and improving the absorbency. The material shall be free from any contaminants and natural coloring matter in the scouring and bleaching treatment. The extent of the pretreatment such as ground whiteness depends upon the  target shade , as brighter and whiter ground whiteness is required for light and bright shades and  dark and dull shades can be dyed on scoured ground without any difficulty.

2. pH of the substrate

pH of the substrate prior to dyeing must be controlled and it should be either neutral or slightly acidic  because if the pH is alkaline at the beginning , the dye molecule may form a permanent bond or premature fixation leading to unlevel dyeing.

3. pH of the dye bath

it should be weakly acidic to neutral  in the dyeing bath in migration and exhaustion phase ,before addition of alkali . It must be checked and regulated because presence of bicarbonates in the water may increase the pH with increase in temperature , which results into partial fixation of the dye molecules resulting in unlevel dyeing. The pH in the fixation stage must be kept at 10.8-11.0 , which shall be achieved by either soda ash alone or a mixture of soda ash and caustic soda.

d.      Solubility of the dyestuffs

It is better to consider the dye solubility chart of individual colors provided by the manufacturer , the dyes with higher solubility are more suitable for better shade and color fastness control.

5. Dyeing temperature

The temperature and rate of rise  of the dye bath affects the affinity of the dye molecules towards fiber, rate of hydrolysis , migration and covalent bond formation. Therefore the dyeing temperature selected must be as per the dye sub class. Effect of temperature on the build up and fixation of individual dyes must be studied to form dyes groups having similar characteristics  and then these groups must be selected for making combination shades. 

f. Electrolyte concentration

The dyes must be exhausted by addition of salt or glauber salt before starting the fixation of color. For electrolyte concentration in the dye bath to be used please refer to tables provided by the dye manufacturers. The electrolyte used must be free from unwanted impurities such as metal salts (iron, copper etc) calcium content , insoluble material ,hardness creating salts.

g. Dyeing time

The dyeing time must be selected based upon the depth of the shade. The timings must be optimized to get  maximum exhaustion as well as maximum fixation of the color in the dyebath. Based on the exhaustion and fixation curves of the individual dyestuffs , an optimum time can be selected . There is no advantage of increasing the fixation time than desired because that will not help either in exhaustion or fixation . Generally darker shades need more time in fixation phase than the lighter shades.

h. material to liquor ratio

The M:L of dyebath affects the dye or shade performance to a large extent , as for as possible robust dye combinations must be used , which are unaffected by the change in liquor ratio . The chemical concentrations must be changed with the change in liquor ratios. If a dye house is having different capacity machines with different M:L ratio then it shall be taken into consideration from the lab recipe stage.

i.Type of alkali for fixation

There are different methods applied to achieve the right pH for the fixation of reactive dyes. Normally soda ash alone is used for the fixation purpose , however a mixed alkali system of soda ash and caustic soda is also used ,particularly in the case of dark shades. A gradual pH change is preferred over the shock change for better dyeing results, therefore a dosing system is strongly recommended in the reactive dyeing to achieve consistent shade reproducibility.

j. Washing off sequence for reactive dyes

The hydrolyesd and unfixed dyes which are present in the dye bath as well as on the fiber after the completion of dyeing cycle, these hydrolyesd dyes have no affinity for the fiber but still they act as direct dyes and in the presence of electrolyte penetrates inside the fiber , with the rise in temperature of washing and soaping. If these are not removed before soaping and washing these  can severely affect the color fastness properties. Such trouble can be reduced or eliminated by following an optimized washing off sequence after dyeing.

The dyed goods must be free from any inorganic salt before going for a soaping treatment . Generally a non ionic soaping agent is used  for soaping purpose to get good washing fastness. An organic acis such as acetic acid is must be used to neutralize the dyebath. The soaping treatment can be done upto a boiling temperature to remove the unfixed and hydrolysed dye effectively. A higher soaping temperature can be selected because  unfixed dye has  practically no affinity for the fiber  and the loosely held dye rapidly diffuse out.  The soaping treatment is recommended in a neutral bath because  under alkaline soaping conditions at higher temperature the dye fiber bond may break and result into loss of color  value due to rupture of dye fiber bond. If the soaping tretment is carried out  efficiently and carefully then there is no need of cationic dyefixing treatment at the end of dyeing cycle

A typical soaping treatment recommended for Procion    XL and XL+ dyes is as shown below

Further Information

Cost reduction in reactive dyeing

A slide show on Reactive dyes click here 

Washing off process by BASF Click Here

Optimizing the process of Reactive Dyeing