Presentation Topic:Briefly discussion about Azoic Dye

DEPARTMENT OF TEXTILE ENGINEERING Course Title :Wet Processing Technology-2

Group-D1.BTX1301002652.BTX1301002583.BTX1301002564.BTX130100285Submitted To:Md.Tanjim Hossain

Azoic dyeAzoic Dyes are also called as Azoic or Napthol Dyes. These AZO Dyes consist a group i.e. called AZO group having two nitrogen atoms and this group (covalent bond) connects atomic ring compounds. The two Nitrogen atoms are bonded with each other and form -N=N- as part of their molecular structure. Azoic Dyes are found mainly in three colors and these are red, brown and yellow.

Another name of Azoic dyeBuilt in DyeMagic ColorDeveloped ColorIce color Napthol Dye

HistoryAzo chromophores were first discovered in 1863 when Martius and Lightfoot coupled diazonium ions and amines. Within the year, Peter Greiss prepared Bismarck brown, the first azo dye. By the 1880s numerous other azo dyes, such as para red and primuline red, were developed.

Since that time, most modern dyestuffs have been derived from diazotized aromatic amines, and hence are sometimes known as diazo dyes. The simplest azo dyes are yellow, but changing the number of chromophores or the backbone structure can produce red, violet, blue and even black dyes. Azo dyes are used as textile colorants, and well as in industrial paints, printing inks, varnishes, plastics, crayons and other products.

. In recent years, many high performance azo pigments have been developed that meet the stringent lightfastness requirements required for artwork (Berrie and Lomax 1997).

Origin Mid 19th century fromGreekazos'without life'

Formation of Azoic DyesThese dyes cannot be applied directly on the fibers as dyes. Actually, these dyes are produced within the fibers itself. For this production, first the fiber is impregnated with one component of these dyes and then the fiber is treated in another component of these dyes. In this way the AZO dyes are formed. This specialty makes these dyes very fast to washing within the fabric market.

When these dyes are used upon the cellulose fabric then initially this fabric starts to suffer from poor rub fastness. This is due to the deposition of the free pigments on the surface of the fabric. This problem can be rectified by boiling the fabric in soap.

Azoic Colors

Azoic Dyeing ProcessAZO Dyeing Process is such a process in which the insoluble azoic dye is produced on the or within the fiber. By treating a fiber with diazoic and coupling components, this process can be achieved. After adjusting the dye bath conditions appropriately, the two above mentioned components react. From this reaction the required insoluble AZO dye is produced.

First Stage:NaptholationSecond Stage:DiazotationThird Stage:Coupling

Step-1:

NaOH ONa27 degree CONH

Sodium Naptholate

Step:2 NH2 N2Cl Conc.Hcl NaNo2 CH3 Cl CH3 ClFast red TR base Diazo component Soluble diazonium salt

Step:3we add sodium naptholate and soluble diazonium salt

CH3

N=N Cl ONa CoNH

Azoic pigment

Naphthols and BasesNaphthol is also known as azoic coupling component. These are acylides are of BON (beta-oxy naphthoic acid). Various types of naphthols can be Naphthol AS, Naphthol ASBS, Naphthol ASBR etc.Base is also known as the Diazotised base. This acts as a coupling reactant along with the naphthol. These are nomenclatured on the basis of color e.g. Fast Red Base. The purpose of diazotisation is to improve solubility.

Dyeing Process of Azoic Colors The Dyeing process is carried out in three successive steps, which are as follows: NaphtholationNaphthol is water insoluble. Thus the process of making insoluble naphthol soluble is known as Naphtholation.

The sodium salt of naphthol obtained above is not very much stable as CO2 reacts with it water to form carbonic acid and it converts it to free naphthol form so we should avoid any type of acidic exposure.

The sodium salt is thus treated with HCHO.

When this methylol compound is exposed to high temperature then it gets converted to methylene compound and naphthol loses its ability to react with diazotised base.The naphthols are classified on the basis of substantivity i.e. low and high substantivity naphthols.

DiazotisationThis process involves conversion of the base in the soluble form i.e. hydrochloride form which has better solubility. R-NH2 + HCl R-NH3+Cl- (Fast base) (Hydrochloride base) HCl + NaNO2 HNO2 + NaCl R-NH+3Cl- + HNO2 R-N+=N-Cl + 2H2O

..At higher temperature, diazotized base formed becomes highly unstable and hence backward reaction starts. Hence the process is carried out at lower temp.We add HCl which reacts with NaNO2 to form HNO2, which helps in diazotisation and reacts with free base to form hydrochloride form.These can be slow coupling bases which require little acidic conditions and fast coupling bases which require stronger acidic conditions.

CouplingThe naphtholated fabric is passed through the diazotised base solution for coupling reaction to take place. This process of coupling is highly exothermic and hence should be carried at low temp. It also requires acidic conditions i.e. it requires 5-6 pH.The CH3COOH besides maintaining the pH also acts as a buffer to maintain the alkalinity of the solution constant.

Coupling Reaction

Some of the naphthol comes out of the fabric and reacts with the diazotised base to give the azoic pigment which reduces the washing fastness. Hence, strong soaping is done to prevent the surface dye. Moreover, azoic colors are not used as the process of applying these dyes is very cumbersome.

Types of AZO dyes in accordance to there natureA. hazardous AZO-dyesB. non-hazardous or safe AZO-dyes

Hazardous AZO-dyes These dyes use AZO-groups as coloring agent, upon cleavage these chemical groups release amines, which are harmful, they are used mostly for cotton dyeing, cheapest alternative to reactive dyes ( best industrial dye ), good color fastness, dyeing process short and easy, pollute waste-water with heavy metals, many AZO-dyes are subject to ISO 14000 legislation

B. non-hazardous or safe AZO-dyesAvailability:...of product:1. not easy to purchase2. not widely distributed3. they are sold by weight and price is higher then hazardous azo dyes...of information:1. information available in English, using international standards

Some Examples

naphthol,beta naphthol pigment,para red,Lithol red,arylide,diarylide,nickel-azo,disazo pigment, andbenzimidazolone

Advantages and DisadvantagesAdvantages of azoic dyesAvailable in bright shades mostly deep red, yellow and orange.Brilliant shape of colourVary from poor to excellent fastness to to light.Fastness to washing, perspiration good to excellent.

Disadvantages of azoic dyesHeavy shades have poor fastness to crocking.High costly

Printing process:The naphtholated fabric is prepared then it is printed with base printing paste by block and screen printing method.After treatment :After printing the printed fabric is dried at 100105 for 510 minute in a dryer.If the naphtholation process is not so sufficient. Then the printing becomes uneven.

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