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Wednesday, March 4, 2015

How to select a Dye

With the enormous host of dyes available to today’s textile industry, the choices are significant. Aside from each coloring agent’s ability to impregnate fibres and fabrics with different color intensities, each has specific functional characteristics that may make it more suitable for one project than for another.
One of the most important decisions that must be made in dye selection is influenced by the products final use. Colorfastness, the degree to which the dye can withstand fading, is crucial in many cases. Washables, for example, must be colorfast so bleeding, the running of color, will not take place when the garment is laundered or used for swimming. Fading is another factor that must be considered, especially when exposed to sunlight, as in the case of active sportswear.

Fabrics that are improperly colored cause numerous problems for mills, manufacturers, retailers, and consumers. One wrong dyeing decision can generate displeasure for every part of the distribution cycle. The consumer returns the damaged product to the merchant, often causing a refund of the purchase price; the retailer, in turn, returns the product to the manufacturer, requesting credit for returned goods; the producer finally becomes embattled with the mill and requests and adjustment.
An in-depth study of the various dye classes and their properties is appropriate for anyone wishing to enter the textile industry – and, for that matter, anyone interested in a career in any aspect of the fashion world. Some of the general classifications are offered to give an indication of their important characteristics to the apparel, accessories, and home furnishings industries.
Excellent to achieve bright colors; not fast to washing, but able to withstand the chemicals used in dry cleaning.
Excellent colorfastness to light and washing; however, the resulting colors are dull.
Bright shades are easily achieved; generally colorfastness to washing and light. Fabrics colored with this dye are usually resistant to crocking; the color will not rub off from friction.
Poor colorfastness to laundering as well as to light penetration; dry cleanable in most cases.
Their potential for colorfastness varies according to the fibres being colored; colorfastness to crocking, perspiration, and dry cleaning is generally good.
Perfect for bright colors; good overall colorfastness, except to chlorine, which eliminates it as a useful agent in the dyeing of swimsuit fabrics.
Bright colors; colorfastness to light varies, depending on the specific makeup of the dye; colorfast to washing.
Excellent colorfastness to sunlight, washing and perspiration.

Thursday, January 1, 2015

Properties and Classification of Acid Dye

Properties of Acid Dye

-         This dye is normally soluble in water.
-         Most of the dyes bear sodium salt of sulphonic acid and carboxylic acid.
-         Dyeing process is normally done in acid medium.
-         Protein fibre like silk, wool and polyamide fibre like nylon etc. are most suitable for dyeing with acid dye.
-         These dyestuffs give varieties of color shade.
-         Color fastness property is good.

Acid Dye

Classification of Acid Dye

According to chemical structure
According to chemical structure analysis we may classify this dye as following ten:
-         Nitro
-         Nitroso
-          Mono Azo
-         Diazo
-         Triphenyl methane
-         Xanthan
-         Azin
-         Quinaline
-         Ketorenine
-         Anthraquinone
According to Application
-         Strong (Class – 1)
-         Weak (Class – 2)
-         Neutral (Class – 3)
Properties of Strong Acid Dye
-         Dye leveling property is very good.
-         Strong acids are generally used in this bath.
-         Its light fastness property is excellent but wet fastness property is not so good.
-         Here we always have to maintain the PH value 2-3.
Ex: Lissmine green
Properties of weak acid Dye
-         Dye leveling property is moderate.
-          Weak acid is used in the dyeing bath.
-         PH value is maintained 5.2 - 6.2.
-         Washing fastness property is good.
-         It can be used for cellulosic fibre dyeing.
Ex: Solway blue – B.N.S
Properties of Neutral Acid Dye
-         Dye leveling power is very poor. So, its usage is very rare.
-         Neutral medium is used for dyeing.
-         PH value around 7.
-         Light fastness property is good.
-         Washing fastness property is also good.
Ex: Coomassic navy blue – 2RNS

Direct Dye

What is Direct Dye?

       An anionic dye which have substantivity for cellulosic fibres, normally applied from an aqueous dye bath containing an electrolyte is known as Direct dye.

Chemical Structure of Direct Dye

Direct Dye

Significance or Properties of Direct Dye

            It is soluble in water.
           It has sodium salt of sulphuric acid or carboxylic acid.
            It has strong affinity to cellulose fibre.
            Protein fibre can be dyed with this dye.
            Comparatively cheap.
            Easily diffusible into fibre.
            Wash fastness is not so good.
            The tinctorial power of this dye is very good.

Classification of direct dye according to application

Based on migration test and salt controllability these dyes are classified as follows –
-         Class – A (Self leveling)
-         Class – B (Self controllable)
-         Class – C (Temperature controllable)
Class – A
-         Dyes migrate well.
-         High leveling power.
-         They may dye unevenly at first but further boiling will bring about even distribution.
Class – B
-         Poor leveling power.
-         Dye exhaustion must be brought about by controlled salt addition.
-         If these dyes are not taken up uniformly in the initial stages, it is extremely difficult to correct the levelness.
Class – C
-         These are not self leveling.
-         Highly sensitive to salt.
-         The exhaustion of these dyes cannot adequately be controlled by addition of salt alone and they require additional control by temperature.

Application of Direct Dye on Cotton Fabric

Typical Recipe
                        Dyestuff – 2%
                        Na2CO3 – 2-3%
                        Wetting Agent – 1%
                        NaCl/Common Salt – 10%
                        M:L – 1:20
                        Temperature – 800-900 C
                        Time – 1-1.5 hrs
Dyeing process
Dye Solution preparation: Mix dye with normal water and make dye paste; then pour hot water to dissolve the dye properly and ensure uniform bath concentration.
-         The dye bath is set at 400C with substrate and required water level.
-         Add wetting agent, sequestering agent, leveling agent, and other auxiliaries and run time 5 min.
-         Add dye solution by linear dosing at 400 C and run time 10 min.
-         Add soda ash by curve or progressive dosing at 400 C and run time 10 min.
-         Temperature has to be raised up to 1000 C (20 C per min.) within 30 minutes.
-         Salt dose is started before reaching the temperature at 1000 C and it continues till reaching 1000 C. It should dosed where exhaustion will be maximum.
-         Dyeing is continued for 60 minutes at 1000 C.
-         Cool down to 700C.
-         Drop the bath, rinse and carry out after-treatment process to improve wet fastness.
After-treatment: The dyed material is carried out at 700C for 30 minutes in a bath containing 1 to 3% of acetic acid (30%) and 1-3% of CuSO4 according to the depth of shade. It improves light and wash fastness.

Trade or Commercial name of Direct Dye

Company Name
Ciba Geigy
Ciba Geigy

Some factors related to this dye

-         PH value – 9-10
-         Temperature – 85-900 C
-         Time – 1-1.5 hrs
-         Effect of dye molecules size – 30-40 A0 (Always lower than the porosity of the of the fibre)
-         M:L or effect of concentration  - Less loss of the solution (For higher – light and for lower – deeper)

Identification of Direct Dye

At first we take 5 gm of colored sample which is provided by the buyer. Then we have to take a test tube with soap or detergent liquor. Then we will also take a white fabric and put both fabrics in the test tube. Then we have to heat it up to boiling point with a burner. After sometimes we can see that the colored sample is colorless and the white fabric becomes colorful. This may only happened for direct dye.

Why Direct Dye is So Called?

These dyes are anionic and having substantivity for all type of cellulosic fibres such as cotton, viscose, rayon etc. These dyes have strong affinity towards the fibre which can be applied directly on the fibre and which do not need any assistance. These dyes have affinity for cellulose and therefore they are also substantive dyes. So, this dye is so called.

Monday, December 15, 2014

Classification of Dyes

Dye is a complex compound which is applied in the textile materials represent color and contains chromophore and auxochrome groups in its chemical structure.

Dye classification

Dyes or dyestuffs are classified according to their chemical structure would form at least 30 classes. The important types are discussed below –

Acid Dyes

This is a large class characterized by their substantively for protein fibres (wool, silk). They are normally applied from an acid dye bath, and hence the name. They are also used for nylon dyeing and printing. ICI trademarks are ‘Lissamine’, ‘Coomasse’, ‘Carbolan’ and ‘Nylomine’ Acid. Acid dyes are anionic, i.e. the dye molecule is negatively charged.

Azoic Dyes

These are used in printing, mainly for cellulosic fibres (predominantly cotton). The characteristic feature of these dyes is that they are formed in situ within the fibre by the reaction of two components, i.e. the diazo component and the coupling component. These components are applied separately, i.e. the coupling component first, followed by the diazo component. A variety of chemical modifications to diazo compounds have enabled them to be mixed with coupling compounds without immediately generating the dyestuff. The dye is formed in a subsequent steaming operation. Trade names are ‘Brenthol’ and ‘Brenthamine’. The former Brentogen range was based on stabilized ‘Brentamine’ and ‘Brenthol’ mixtures, acid steaming being needed to form the dye. Ordinary steaming suffices to develop the ‘Neutrogen’ and ‘Rapidogen’ brands.

Basic Dyes

These dyes are cationic, i.e. the dye molecule is positively charged. To apply them to cotton it provide necessary to give a tannin mordanting treatment. The resulting fastness of the dyes was still only moderate and the style is now virtually obsolete. Basic dyes may be applied to wool and silk without mordant, but again the results are characterized more by brightness than fastness. Specially developed basic dyes are widely used on acrylic fibres, upon which they are quite fast. The ICI trade mark is ‘Synacril’.

Direct dyes

The name arose from the fact that the dyes possessed direct substantivity for cotton, i.e. without the necessity for a pre-mordanting treatment. A wide range is available both in color and in fastness. The limiting factor for these dyes in printing is their lack of washing fastness even when given one of the various after treatments available. ICI trademarks are ‘Chlorazol’ and ‘Durazol’.

Disperse dyes

These are water insoluble dyes sold as aqueous dispersions or as re-dispersible powders or grains. They were originally introduced for the dyeing of cellulose acetate. Modern disperse dyes are printed on ‘Terylene’ polyester fibre, cellulose acetate and cellulose triacetate. ICI trademarks are ‘Dispersol’, ‘Duranol’ and ‘Procinyl’ (disperse reactive type).

Mordant Dyes

These are are applied to the fibre in conjunction with a metal salt. The dye-metal complex possesses greater fastness than the dye alone. In spite of the fact that basic dyes were applied to cotton by means of a tannin-antimony mordant it is conventional to exclude such dyes from the mordant group. Similarly exclude are direct dyes requiring a metallic salt treatment to obtain full fastness. Some mordant dyes are of great antiquity many used even fifty years ago were of natural origin. Turkey reds, madder and alizarin reds all relied on an aluminium mordant while logwood blacks were based on iron. Chromium acetate was widely used in admixture with mordant dyes for cotton printing. These dyes are only very rarely encountered in modern textile printing.

Pre-metalized Dyes

These may be regarded as a later development of mordant dyes. Prior to their discovery wool had been mordant dyed by three processes –
     -         Applying a chromium salt to the wool before the dye (chrome mordant method).
     -         Applying the dye first and after treating with a chromium salt (the after chrome method).
     -         Applying the dye and chromium salt simultaneously (the Meta chrome method).
The difficulty especially in the after chrome method was due to color matching in the presence of an appreciable shade change. This led to research on performed dye-metal complexes. Swiss and German manufacturers achieved the first real success on wool in 1915, and introduced ranges of 1:1 chrome complex dyestuff. The strong acid necessary to dye these products led to further work. By linking chromium with two molecules of dye, the 1:2 chromium complexes were formed. These were easier to apply and are widely used in dyeing and to a lesser extent in printing. Trademarks are ‘Irgalan’ and ‘Cibalan’.

Onium Dyes

A small range of dyes which owe their name to the fact that they are either ammonium or sulphonium compounds. They are water soluble cationic dyes and hence must not be mixed with anionic dyes; otherwise they will participate with each other. In the presence of heat and alkali the solubilising groups split up to give a very fast dye on the fibre. This is an example of a temporarily solubilised dyestuff. Cotton is the most important fibre for onium dyestuff. The ICI trademark is ‘Alcian’.

Pigment Dyes

These products are insoluble in water and are preferably also insoluble in white spirit and in chlorinated solvents used in dry cleaning. In admixture with a suitable resin binder they may be printed on the majority of the textile fabrics. In recent years extensive research especially in USA and Germany has produced greatly improved binders. This has resulted in prints of much softer handle as well as better wet and dry rubbing fastness. The trademarks are ‘Aridye’ and ‘Hifast’ (Inmont, USA), ‘Acramin’ (F, Bayer), and ‘monolite’ and ‘Monastral’ (ICI).

Oxidation Dyes

In principle, a small molecular weight intermediate is treated under acid oxidation conditions to form a much larger colored molecule. These products have been most widely developed as hair and fur dyes. In printing, aniline black is still of importance, while diphenyl black is now little used although a solubilized derivative of the starting intermediate ‘Solonile’ black is of value in certain styles. Paramine brown, one of the few other oxidation colors formerly employed in textile printing, fell out of general use on fastness grounds.

Reactive Dyes

First marketed by ICI in 1956, this group of dyes owes their name to their ability to undergo a chemical reaction with cellulose fibres. This produces a covalent dye-fibre bond which gives dyeing and prints of excellent washing fastness. Reaction with wool and silk is also possible, while on nylon, although some of the dyes fix well, the molecular size of some of the others is too large to penetrate the nylon efficiently. Reactivity and hence dye stability may vary widely. It is usual to indicate differences in reactivity either by using two trademarks or by using two different letters and a single trademark, e.g. ‘Procion’ M (more reactive) and ‘procion’ H (less reactive) dyes.

Sulphur Dyes

These products may be dyed to give fabrics of good washing fastness at low cost. As a range they have never been successful in textile printing owing to erratic fixation. An exception is the sulphur black ‘Indicarbon’ CL (Casella) and its equivalents. These are printed alongside the cheaper members of the vat range where all round fastness requirements are not excessively stringent, e.g. dress goods, but not furnishings.

Vat Dyes

These are insoluble in water and contain keto groups. In alkaline solution a reducing agent, e.g. sodium hydrosulphite will produce a soluble leuco compound. It is the sodium salt of the leuco compound which dyes into the fibre. To obtain the vat dye back in its original form an oxidation treatment is necessary. Indigo is a vat dye and synthetic sulphur containing derivatives are termed thioindigoid vat dyes. The other and larger vat dye groups are termed anthraquinonoid vats. This broad classification is often used as the basis of dividing the dyes into two ranges by using two trademarks, e.g. ‘Durindone’ (for indigoid and thioindigoid vat dyes) and ‘Caledon’ (for anthraquinonoid vat dyes).
An Introduction to Textile Printing
By_ W Clarke

Thursday, August 14, 2014

Hydrolysis of reactive dye

Hydrolysis is a chemical process in which a molecule is cleaved into two parts by the addition of a molecule of water. One fragment of the parent molecule gains a hydrogen ion (H+) from the additional water molecule. The other group collects the remaining hydroxyl group (OH−).

Hydrolysis of reactive dye
During the application of reactive dyes to cellulose fibers under highly alkaline conditions, a competing hydrolysis reaction takes place, originating in the non-reactive oxi-dye form, which is lost for dyeing, and passes into the waste water.
Unfixed or hydrolyzed reactive dye has to be washed off thoroughly in order to achieve the desired superior wet fastness of the reactive dyeing. As much as 50% of the total cost of a reactive dyeing process must be attributed to the washing-off stages and treatment of the resulting effluent. This aspect of the process should be recognized as a major limitation that prevents reactive dyes from achieving the degree of success that was predicted for them at the time of their discovery.
1.      In case of Triazinyl dyes:
During the application of reactive dyes to cellulose fibers under highly alkaline conditions, a competing hydrolysis reaction takes place.

2.       In case of Vinyl Sulphone Dyes:
Dye-SO2CH = CH2 + HO – cellulose ® Dye – SO2 CH2 -CH2 O cellulose
Dye-SO2CH = CH2 + H-OH ® Dye-SO2 CH2-CH2 OH
For preventing hydrolysis the following precautions are taken
  1. As hydrolysis increases with increasing temperature during dissolving and application temperature should not be more than 40°C.
  2. Dye and alkali solution are prepared separately and mixed just before using.
  3. Dye and alkali should not be kept for long time after mixing.
Exhaustion, Fixation & Hydrolysis

During the application of reactive dyes to cellulose fibers under highly alkaline conditions, a competing hydrolysis reaction takes place.

  1. The percentage of hydrolyzed dye exhausted onto the fibre: 16% & 9%
  2. The percentage of dyes I & II actually Fixed: 68% & 66%
  3. The percentage of hydrolyzed dye dropped with the dye bath: 16% & 25%
Together (2+3) indicates the percentage of wasted color: 32% & 34%
Dye Hydrolysis In and Out the Fibre
During the application of reactive dyes to cellulose fibers under highly alkaline conditions, a competing hydrolysis reaction takes place.

Factors Affect Dye Hydrolysis
  • Liquor Ratio: Longer liquor ratio increases Hydrolysis and vice versa.
  • Salt Concentration: Higher Salt Concentration decreases Hydrolysis upto a limit and vice versa.
  • PH: Higher PH Increases Hydrolysis and vice versa.
  • Temperature: Higher Temperature increases Hydrolysis and vice versa.
  • Dye Reactivity: Increase both hydrolysis & fixation rate.
  • Dye Substantivity: More substantive dye cause more hydrolysis but if substantivity is reduced to bare minimum or removed altogether, the build-up problem arises during dyeing and color yield problem (dyeing) of the dye is reduced considerably.
  • Time: Higher Dyeing time increases Hydrolysis and vice versa.
  • Type & number of Reactive Group: VinylSulphone is more prone to hydrolysis than Triazinyl group.
  • Types of bridging group: The oxide (O-) and sulphide bridges are less stable in alkaline hydrolysis. But more stable bridges decreases reaction rate along with the hydrolysis.
Hydrolysis & no of Reactive groups in a Reactive Dye
Covalent bond formation and hydrolysis take place concurrently during the dyeing of cellulose with a reactive dye. Clearly if the dye has only on reactive group, hydrolyzed product can no longer take part in the dyeing. However if the dye has more than one reactive group, it will contain further groups for opportunity for fixation.
Additional reactive groups do offer the important benefit of potentially increasing the fixation of a dye.
If the probability of fixation of each reactive group is, for example 60%, and if it is assumed that hydrolysis of the first reactive group does not alter the physical or chemical properties of the dye the probability of dye-fibre bond formation of a bifunctional dye is 84%[60+(0.6×40)]. Although all structural stages to a dye impact on its dyeing behavior some extent a multifunctional dye has a fixation potential than a nonfunctional reactive dye.
Potential Problem Due to Dye Hydrolysis
1)  Hydrolysis accompanies fixation, resulting in incomplete utilisation of dye. Hence dye wastage occurs. Up to 40%-60% dyes (Avg. 50%) are wasted in this case.
2)  Relatively large amounts of electrolyte are required for exhaust, otherwise dye hydrolysis will occur greatly in dye bath.
3)  Laborious removal of unreacted and hydrolysed dye is required – often a longer operation than the dyeing step itself and not always entirely satisfactory.
4) Longer washing operation for removal of unreacted and hydrolyzed dye often costs 50% of total dyeing cost.
5)  Hydrolyzed dye is discharged as coloured effluent, and effluent cost is risen up. Moreover, Color is not easily removed by effluent treatment processes and in many cases the dyes are not readily biodegradable
6) Hydrolyzed, unfixed halo heterocyclic reactive dyes may pose an environmental hazard (AOX).
7)  De spite reactive dyes being covalently bound to the substrate, fastness problems associated can occur due to hydrolysis.
8)   Less Storage ability.
9)   Trailing Problem for continues dyeing. 
10)  Running Shade in batch process. 

Tuesday, January 28, 2014

Notes on Sulphur Dye

Significance /properties of Sulphur Dyes | Chain formation of Sulphur Dye | Remarks/precautions of Sulphur Dyes | Deffects of sulpher dye | Application of Sulphur dye on cotton goods | Chemical structure of sulphur dye | Commercial name of sulphur dye | Test method of sulphur dye

Q. Write down the significance/properties of Sulphur Dyes.
 Ans. Significance of Sulphur Dyes:

Wednesday, January 15, 2014

Notes on Azoic dye

Definition and properties/significance of Azoic Dyes | Why is azoic color called ‘Ice’ and ‘Magic’ color? Also ‘Napthol’ and ‘Pigment’ color? | Description of the general procedure for dyeing cellulosic material | What is Diazotization? | Write down the function of different chemicals used in Napthol Dyeing |Distinguish between Fast Salt and Fast Base |  Explanations of  the stripping method  | Precaution/Remarks is taken while dyeing  |  Trade name and chemical Structure  | Describe the test method of Azoic color

Q. Write down about Azoic Dye?
The dyes containing azo groups – N = N – are called Azoic Dye. These are not ready made dyes but are produced by reaction of two components – Diazocomponent or Base/Salt and coupling component (Napthol). Azoic dye also named as Napthol, Branthol, Magic and Ice color.
Dye formation in fiber occurs on the basis of coupling reaction.

RN2Cl + Rʹ -ONa → R-N=N-Rʹ -OH
Normally two baths are needed for dyeing.
1. Impregnation bath.
2. Developing bath.

Q. Explain the properties/significance of Azoic Dyes.
Ans. Properties/significance of Azoic Dyes:
● These dye stuffs always contain Azo groups in its chemical structure.
● Light fastness property is admirable.
● Brightness of shade is also admirable.
● It is directly insoluble in water.
● These dye stuffs are always used in dyeing cellulosic material.
● Here dyeing operation is completed by two bath arrangement. One is called     impregnation bath and another is called developing bath.
● Alkali resistance is poor to good, Index 2 – 4.
● Suitable for lighter shade dyeing (Light resistance: Poor to very good, Index 2 – 7).
● This dye stuff is called developed dye due to formation of dye in fiber during dyeing process.
●Addition of salt increases the substantivity.
● Napthol dispersed in alcohol, T.R. oil.

Q. Why Azoic Dye is so called?
Ans. This color contains insoluble azo groups in its chemical structure.
– N = N –
Azo group
    That’s why this color is called Azo color.

Q. Why is azoic color called ‘Ice’ and ‘Magic’ color?
 Ans. Ice Color:
          The coupling component is finally soluble in diazotization reaction. Diazotization is a chemical reaction where the  base (Aromatic Amine) is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C).
Why the azoic color is called ice and magic color?
That’s why this dye is called Ice color.
Magic Color:
Two steps are required by dyeing with azoic color. In the first step textile goods are dyed by Napthol color. In the 2nd bath, Base or Salt is used for dyeing. After 2 – 3 minutes dyeing in 2nd bath, the azoic color is seen in the textile goods magically. For this reason this dye is called Magic color. 
Q. Why Azoic dyes are called ‘Napthol’ and ‘Pigment’ color?
Ans. Napthol color:
Azoic coupling components are insoluble in water. To make them soluble in water the textile materials are impregnated in a solution of Napthol and NaOH. As the first coupling component is Napthol color.

          Pigment color:
          Azoic dyes contain Azo group and final color is insoluble in water, so it is called Aoic Pigment.
                                        Base   +     Napthol Azoic dyes
                                     Soluble         Soluble         Insoluble
Q. Describe the general procedure for dyeing cellulosic material with Azoic Dyes.
Ans. General Procedure for dyeing cellulosic material with Azoic Dyes:
           Two bath of individual recipe is used for dyeing with azoic dyes.
1.     Impregnation Bath.
2.     Developing Bath.
Impregnation Bath (1st bath):
Dye Stuff → 3% (According to the wt of the material)
NaOH → 2%
T.R. oil → 2%
Hot water → 3 times
Cold water → 7 times
HCHO → 1.5%
Temperature → 40˚C – 50˚C
Time → For a few minutes (2 – 3)
Developing Bath (2nd bath):

Salt Bath
Fast salt → 6%
Hot water (30˚C – 40˚C) → 2 times
Cold water → 8 times
NaCl → 2% – 3%
Time → 2 – 3 minutes

Base Bath
Fast base → 3%
HCl → 2.5% - 3%
NaNO2 → 1.5%
Cold water → 10 times
Temperature → 0˚C – 5˚C
Time → 15 (2 – 3) minutes
In major cases, we use base bath. It gives very good color in low cost though it is insoluble in water.
Dissolve NaOH in small quantity of hot water with Napthol & T.R. oil in a bath and make a paste. Then add slowly in it, the rest hot water and stir (mix) constantly. After dissolving color perfectly and above mentioned cold water and finally the solution of Napthol is thus obtained, this is cooled to 50˚C if necessary, HCHO may be added in the impregnated bath. Now the bath is ready for steeping textile goods for a few minutes (In this bath, any naptholated goods, excepting the napthol AS – G will look yellow).

In the developing bath salt is dissolved with hot water and then cold water added in the bath. Finally add NaCl in the developing bath. Now treating the above naptholated or impregnated goods for 2 – 3 minutes in this bath. It will be noted that the color will develop the goods magically. Then squeeze the goods and boiling it in a soap bath followed by washing & drying. Now steep the textile goods for a while after developing a bath contains 1.5% of HCl in times of water. It is done only for neutralization of goods. Finally 3% soap and 1.5% soda is taken in a bath containing 15 times and treat the goods for a few minutes and wash the goods in fresh plain water. Then squeeze and dry. In this way, dyeing procedure is completed.

Q. What is Diazotization?
Ans. Diazotization:
          It is a chemical reaction where the fast base is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C).

Diazotization is a chemical reaction where the fast base is to be converted to a solubilized form by the chemical reaction with NaNO2 at ice temperature (0 – 5˚C). 
Q. Write down the function of different chemicals used in Napthol Dyeing.
Ans. Function of different chemicals used in Napthol Dyeing:
Caustic Soda:
à        Soluble the dye material.
à        Produce alkali medium.
T.R. oil:
à        Used as softening agent.
à        Used as dispersing agent.
à        Ensure the actual level dyeing properties.
à        For proper dyeing.
à        To increase the substantivity of the azoic color in textile materials.

Q. Distinguish between Fast Salt and Fast Base
Ans. Comparison between salt and base used in azoic dye:
Fast Salt
Fast Base
1) Fast salts are normally soluble in water.
1) Fast salts are normally insoluble in water.
2) Fast salts reacts diazonium base in its chemical structure.
2) Fast base reacts aromatic amine group in its chemical structure.
3) No extra process required to solobulize the salt.
3) NaNO2 and HCl are required for solobulize the base to produce the diazonium salt.
4) A huge amount of salt is required in developing bath.
4) A little amount of base is required in developing bath.
5) In salt bath additive material is must required.
5) In base bath additive material is not required.
6) Color fixation is poor in case of salt bath.
6) Color fixation is very good in base bath.
7) Fast salt is comparatively costly.
7) Base is comparatively cheaper. 

 Q. Explain the stripping method of Azoic color.
Ans. Stripping method of Azoic color:
NaOH → 4% (According to the wt of the material)
Na2S2O4 → 6%
Lissol Amine – A → 2% (Stripping promoter)
Water → 20 times
Time → 20–30 minutes
Temperature → Up to boiling (100˚C)

Azoic dye stuffs once developed are very difficult to strip. The yellow combination with AS – G and those with napthol of high substantivity are the most difficult one to strip. In order to affect satisfactory stripping Lissol Amine – A is used. It acts as a stripping promoter, when used in conjunction with a reducing agent like sodium hydro-sulphide and alkali.

The dyed material treated in a bath containing Lissol Amine – A, NaOH and sodium hydro – sulphide. 20 times of water of the dyed material is added. Now boil for 20 to 30 minutes until the shade is reduced to a pale (Light) yellow or brown color. The quantity of hydro – sulphide is increased in the case of yellow combination. 

Q. Write down the Precaution/Remarks is taken while dyeing with Azoic Dyes.
 Ans. Precaution/Remarks are taken while dyeing with Azoic Dyes:
                   i. Impregnation bath liquor can be preserved for a day or two days.
                ii. Developing bath liquor cannot be preserved for a day.
               iii. Naptholation material should never allow to come in contact with acid, alum and sunray.
               iv. Generally 2 – 3 minutes duration is suitable for both impregnation and developing bath.
                 v. If any way impregnating and developing liquor mixed together, the entire nature will be inactive and useless.
               vi.  During dyeing of protein fiber (Silk, Wool) with azoic dye, we should be very careful not to damage the protein fiber due to high alkali concentration.
                vii. Bases yield comparatively better performance than salt.

Q. Write down five Trade name of Azoic color.
Trade Name
Ciba Naphol
Igra Napthol
Nacco – thol

Q. Show the chemical Structure of Azoic Dye.
Ans. Chemical Structure of Azoic Dye:

The chemical Structure of Azoic Dye.
Q. Describe the test method of Azoic color.

Ans. Test method:
           Take a sample dyed or printed with azoic color in a test tube in the presence of a reducing agent named Sodium Hydro/Bisulphide water liquor. Now treat the sample up to boiling stage. Then we will observe the color will come out completely from that sample. Now this liquor and sample are to come in an oxidizing action in the presence of air or an oxidizing agent. If the color is not received to it, then it will indicate that the sample are dyed or printed with azoic color.

        i. All the chemicals according to the recipe are mixed with water to make a suitable solution.
     ii. At definite temperature (0˚C–5˚C), if the material treated with this for 15 to 20 minutes then light brown color will be arise. This is known as diazotization.
   iii. To remove excess HCl we should use Na – Acetate.
To protect from sunlight, we can use Al – sulphate.]

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