Tuesday, 28 April 2015

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Direct Dye

Direct Dye

Direct Dye
Direct Dye
Direct dye is a class of dyestuffs that are connected specifically to the substrate in an impartial or soluble shower. They create full shades on cotton and linen without mordanting and can likewise be connected to rayon, silk, and fleece. Direct dyes give brilliant shades however show poor washfastness. Different aftertreatments are utilized to enhance the washfastness of direct dyes, and such dyes are alluded to as "aftertreated direct dyes."Direct dyes are particles that stick to the fabric atoms without assistance from different chemicals. Direct dyes are characterized as anionic dyes with substantivity for cellulosic strands, typically connected from a fluid dyebath containing an electrolyte, either sodium chloride (NaCl) or sodium sulfate (Na2SO4).. 

the direct dyeing procedure with direct dyes is extremely straightforward, Direct dyeing is regularly done in a nonpartisan or slight soluble dyebath, at or close breaking point , however a different aftertreatment, for example, cationic dye altering , to upgrade wet quickness has been important for most direct dyeing . 

Direct dyes are utilized on cotton, paper,leather, fleece, silk and nylon. They are likewise utilized as pH pointers and as organic stains.

Chemicals Nature of Direct Dyes:

Synthetically they are salts of complex sulfonic acids.

Structure:-More than 75% of every direct dye are unmetallised azo structures, incredible dominant part of them are disazo or polyazo sorts.

Ionic Nature:-Their ionic nature is anionic.

Solvency:-They are dissolvable in water .

Proclivity:-They have a liking for a wide mixture of filaments, for example, cotton ,thick, silk jute ,cloth and so forth.. They don't make any changeless concoction bond with the cellulosic strands however are connected to it through extremely week hydrogen holding and also vander waals powers. Their level shape and their length empower them to lie close by cellulose strands and expand the Van-der-Waals, dipole and hydrogen bonds.

Sorts of Direct Dyes: 
The SDC characterization of direct dyes is takes after

(1) Class A – dyes that are self-leveling, i.e. dyes of good relocation or leveling properties.

(2) Class B – dyes that are not self-leveling, but rather which can be controlled by expansion of salt to give level results; they are depicted as salt-controllable.

(3) Class C – dyes that are not self-leveling and which are exceedingly delicate to salt, the depletion of these dyes can't enough be controlled by expansion of salt alone and they oblige extra control by temperature; they are depicted as temperature-controllable.

Utilization of Direct Dyes 
Direct dyes are generally connected with the expansion of electrolyte at or close to the bubble in the machines fit for running at air weight .Yet in HTHP dyeing machines it is done at temperatures over the bubble in the event of immaculate and mixed yarns.

An expansion of antacid, for the most part sodium carbonate, may be made with acid-touchy direct dyes and with hard water and to upgrade the dye solubilisation. At the point when cellulose is inundated in an answer of a direct dye it retains dye from the arrangement until balance is accomplished, and at this stage a large portion of the dye is taken up by the fiber. The rate of retention and balance depletion shift from dye to dye. The substantivity of the dye for cellulose is the extent of the dye consumed by the fiber contrasted and that staying in the dyebath.

Dyeing Strategy 
The shading is glued well and broke up in bubbling water to get a bump free arrangement .An expansion of 0.5–2 g l–1 sodium carbonate may be worthwhile when applying dyes of just direct solvency in full profundities.

The dyebath is situated at 40°C,

Raise to the bubble at 2 degC min–1

Hold at the bubble for 30–45 min,

Amid hold include 10–15 g l–1 of sodium chloride or calcined Glauber's salt. Light shades are dyed without or lesser expansion of salt.

Enhanced yields can be attained to when applying full profundities by cooling to 80°C toward the end of the period at the bubble, including a further 5 g l–1 salt and ascending to the bubble once more

Dye shower variables which must be considered for level dyeing,

1.Temperature of Dyeing and rate of warming

2.Electrolyte focus and expansion


4.Dye dissolvability

5.Use of leveling specialists

After Treatment of Direct Dyed Material

The wet speed properties (especially washing, water and sweat) of basically all dyeing of direct dyes are insufficient for some end utilizes yet remarkable enhancements can be realized by after medicines.

Diazotisation and advancement

Metal salt medicines

Cationic altering operators

Formaldehyde treatment

Cross connecting specialists and pitch medicines

Stripping:- Most direct dyes can be stripped of the utilization of stripping salts (Sodium Hydrosulphite) and/or by utilizing a chlorine fading operators, for example, sodium hypochlorite, without hurtful consequences for the strands.

Shading speed properties of Direct Dyed material: For the most part these dyes are utilized where high wash quickness is not needed.

Wash Speed: Poor unless treated with suitable dye altering operators and/or quickness enhancing completing specialists.

Light Speed:-Great
Rubbing Speed: Moderate to Great 


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