Wednesday, December 30, 2009

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.

Tuesday, December 29, 2009

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.

(D) Rinse at 90-100 º C (10 min.)

(E) Rinse cold and finish accordingly.

Dyeing with Direct dyes

Dyeing Method With Direct Dyes

Direct Dyes

Direct Dyes are used in wide range of dyeing applications such as on Cotton, Silk and Viscose Fabrics. Direct dyes are Famous for their easy application, leveling property, good brightness and fastness. These dyes can be safely applied on Textiles and Leather.

PRE - TREATMENT

Good pre-treatment is essential if satisfactory dyeing is to be obtained. To get better depth and fair brightness, Grey Fabrics must be free from impurities like sizing materials and spinning oil by boiling the Grey with alkline or some times bleaching also carried out in case of pale shades.

METHOD OF DYEING

(1) DISSOLVING THE DYESTUFF

The dyestuff is pasted with cold water and dissolved by pouring 50 to 100 times its weight of Boiling water while stirring. The solution may be boiled to ensure complete dissolution. For Certain dyes, which are dyes from and alkline dye bath, it is preferable to add half its weight of soda ash while pasting with water.

(2) YARN DYEING

Set the Dye Bath at 50°-60° C temperature with dyes solution, salt and soda ash. Run for 15 Minutes. Gradually raise Temperature to 90°-95° C. Run for 30 to 45 minutes. In order to Overcome un level dyeing salt may be added in installments after about 15 minutes of initial dyeing prior to raising the dye bath temperature.

In the case of dyestuff which possess maximum affinity at temperature below boil, it is preferable to start dyeing at boil, dye for 15 to 20 minutes and then add salt in two installments to exhaust the bath and continue dyeing in a cooling bath (60° c) for 15 to 20 minutes.

JIGGER DYEING

The dyeing on the Jigger is carried out as follows:-
First End : 1/2 quantity of Dyes solution, soda ash and 1/4 quantity of Salt at room Temperature. Second End : 1/2 quantity of Dyes solution, 1/4 quantity of Salt at 60°)c, raised to 80°c.Third End : 1/4 quantity of Salt.
Fourth End : 1/4 quantity of Salt.

The temperature is raised to raised to boil and four ends are given at boil. Finally the dye-liquor is Drained and further two ends are given in cold water.

AFTER TREATMENT

Fastness to wet treatments can be improved by after treatment with 1-2% Cationic Dye Fixing Agents at 40-50° c for minutes.
In case of some selected dyes, light fastness can be improved by after treatment with:-1-2% Copper Sulphate1-2% Actic (30%) at 80° c Temperature.

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

pretreatment of the substrate
pH of the substrate prior to dyeing
pH of the dyebath
solubility of the dyestuff
dyeing temperature
electrolyte concentarion
dyeing time
M:L
Type of alkali
Washing off sequence
Quality of water and salt

The detail of impact of above parameters,

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.

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.

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.

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

Monday, December 28, 2009

Dyeing Machines

Cabinet Hank Dyeing Machines

Roller Hank Dyeing Machines

Spray Hank Dyeing Machines

Hank Dyeing in HTHP Machines

HTHP Vertical Package Dyeing

HTHP Horizontal Package Dyeing

Beam Dyeing machines

Jet Dyeing Machines

Jiggers

Winch Dyeing machines

Soft Flow Dyeing Machines

Paddle Dyeing Machines

Yarn Printing Machines

Dyeing machines

Fabric printing Machines

Machines

Dyeing machines

dyes

Direct Dyes

Direct Dyes are molecules that adhere to the fabric molecules without help from other chemicals. Direct dyes are defined as anionic dyes with substantivity for cellulosic fibres, normally applied from an aqueous dyebath containing an electrolyte, either sodium chloride (NaCl) or sodium sulfate (Na2SO4).. The dyeing process with direct dyes is very simple, Direct dyeing is normally carried out in a neutral or slight alkaline dyebath, at or near boiling point , but a separate aftertreatment such as cationic dye fixing , to enhance wet fastness has been necessary for most direct dyeing .

Direct dyes are used on cotton, paper,leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.

Chemicals nature of direct dyes

Chemically they are salts of complex sulfonic acids.

Structure:-More than 75% of all direct dyes are unmetallised azo structures, great majority of them are disazo or polyazo types.

Ionic Nature:-Their ionic nature is anionic.

Solubility:-They are soluble in water .

Affinity:-They have an affinity for a wide variety of fibers such as cotton ,viscose, silk jute ,linen etc.. They do not make any permanent chemical bond with the cellulosic fibers but are attached to it via very week hydrogen bonding as well as vander waals forces. Their flat shape and their length enable them to lie along-side cellulose fibers and maximize the Van-der-Waals, dipole and hydrogen bonds.

Types of direct dyes

The SDC classification of direct dyes is follows

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

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

(3) Class C – dyes that are not self-levelling and which are 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; they are described as temperature-controllable.

Application of Direct Dyes

Direct dyes are usually applied with the addition of electrolyte at or near the boil in the machines capable of running at atmospheric pressure .But in HTHP dyeing machines it is carried out at temperatures above the boil in case of pure as well as blended yarns.

An addition of alkali, usually sodium carbonate, may be made with acid-sensitive direct dyes and with hard water as well as to enhance the dye solubilisation. When cellulose is immersed in a solution of a direct dye it absorbs dye from the solution until equilibrium is attained, and at this stage most of the dye is taken up by the fibre. The rate of absorption and equilibrium exhaustion vary from dye to dye. The substantivity of the dye for cellulose is the proportion of the dye absorbed by the fibre compared with that remaining in the dyebath.

Dyeing Method

The color is pasted well and dissolved in boiling water to get a lump free solution .An addition of 0.5–2 g l–1 sodium carbonate may be advantageous when applying dyes of only moderate solubility in full depths.

The dyebath is set at 40°C,

Raise to the boil at 2 degC min–1.

Hold at the boil for 30–45 min,

During hold add 10–15 g l–1 of sodium chloride or calcined Glauber’s salt. Light shades are dyed without or lesser addition of salt.

Improved yields can be achieved when applying full depths by cooling to 80°C at the end of the period at the boil, adding a further 5 g l–1 salt and rising to the boil again.

Dye bath variables which must be considered for level dyeing,

1.Temperature of Dyeing and rate of heating

2.Electrolyte concentration and addition

3.Time

4.Dye solubility

5.Use of leveling agent

After treatment of Direct dyed material

The wet fastness properties (particularly washing, water and perspiration) of virtually all dyeing of direct dyes are inadequate for many end uses but notable

improvements can be brought about by after treatments.

Diazotisation and development
Metal salt treatments
Cationic fixing agents
Formaldehyde treatment
Crosslinking agents and resin treatments

Stripping:- Most direct dyes can be stripped of the use of stripping salts (Sodium Hydrosulphite) and/or by using a chlorine bleaching agent such as sodium hypochlorite, without harmful effects on the fibres.

Color fastness properties of Direct Dyed material:- Generally these dyes are used where high wash fastness is not required.

Wash Fastness:- poor unless treated with suitable dye fixing agent and/or fastness improving finishing agent.

Light Fastness:-Good

Rubbing Fastness:- Moderate to Good

Chemical Wash Fastness:- Poor

How to Identify a Direct Dye on a Substrate Dye class identification

How to test comparative strength of a cationic dye fixer

Azo Group A slide show

Chemistry of dyes