wet processing engineering( dyes) Sulphur dye

Sulphur dye

1. Sulphur Dyes

2. What is Sulphur Dyes? Sulphur dyes are complex heterocyclic molecules or mixtures formed by melting or boiling organic compounds containing amino or nitro groups with Na- polysulphide and Sulphur . Sulphur dyes are so called as they all contain Sulphur linkage within their molecules. The sulphur dyes are named so because of the presence of sulphur atoms in their molecules. Like direct dyes, sulphur dyes are also quite cheap for dyeing cellulosic textiles with limited color fastness properties. Different types of sulphur dyes include: CI sulphur dyes CI leuco sulphur dyes CI solublized sulphur dyes CI condensed sulphur dyes

3. Sulphur dyes are highly colored , water insoluble compounds and have to be converted in to water soluble substantive forms ( lucoforms ) before application to the textile materials. This conversion is carried out by a treatment with a reducing agent like dilute aqueous Na 2 S . Since this lucoform of Sulphur dye is substantive to cellulosic materials. They are absorbed on the fiber surface. Then they are reconverted original water insoluble form of dye by oxidation. This oxidation is carried out by “airing” (exposure to air) or by using an oxidizing agent like Na-dichromate (Na 2 Cr 2 O 7 ). The reducing agents converts the “S” in dye in to –SH group and the Sulphur linkages. Then inside the material the thiols containing –SH groups are oxidized & thus reconverted to original form of dye.

4. This is shown in the bellow: Sulphur gives best result (Bright Tone) when they are used to produce black, Black and brown shades but red shades cannot be obtained by Sulphur dyes .

5. History of Sulphur Dyes The history of Sulphur dyes may be summarized as below: The first Sulphur dyes where made in 1873 heating saw dust, caustic soda and Sulphur . It occurred by chance when a reaction vessel containing Na 2 S was leaking and the saw dust was used to wipe the solution coming out. Later a cotton fabric come in contact with this contaminated sawdust and become stained. The real pioneer of Sulphur dyes was vidal who produce vidal black (Name of Sulphur dye) by fusing para-phenylene diamine with Na 2 S & Sulphur in 1893. In 1897 Kalischer produced Immedial Black FF by heating 2, 4-dinitro-4-dihydroxy diphenylamine with Na-poly sulphide . In 1896 Read Holliday introduced a range of grey, brown and black Sulphur dyes by the action of Sulphur , alkali sulphides and many organic compounds.

6. Trade Names Name of Manufacturer Country of origin Calcogen Dyes Dept. American Cyanamid Co. USA Pyrogene Ciba Switzerland Thional Sandoz Switzerland Solfo ACNA Italy Sulfogene Du pont USA Thional Imperial UK Mitsui Sulphur Mitsui Chemicals Ind. Co. Ltd Japan

7. Properties of Sulphur Dyes: The main properties and characteristics features of Sulphur dyes are mentioned below:- Sulphur dyes have Sulphur linkage within their molecules. Sulphur dyes are highly colored water insoluble dyes. Some dyes are partially soluble in water. They have no direct affinity towards cellulosic fibers. To make them substantive they are to be converted in to soluble lucoform by treating them with reducing agents (Like dilute Na 2 S solution) Sulphur dyes have good light fastness with rating about 4. This light fastness may be improved by an after treatment with metallic salt. These dyes have excellent wash fastness with rating about 3-4. This good wash fastness is due to its larger molecular size & insolubility in water. They are not applicable to wool due to strong alkaline condition. They are exclusively amorphous, few of them show crystallinity . Important for producing a wide range of shades on a verity of cotton and rayon. Sulphur dyes are suitable for heavy & durable shades Available in powder and soluble form Sulphur dyes are cheap & easy to manufacture. Heat and chemical resistance of Sulphur dyes are moderate to good. They have poor fastness to chlorine and are not applied to goods which are bleached with hypochlorite.

8. Features of Sulphur Dye Amorphous Colloidal materials. High molecular weight with various composition Complex molecular structure –heterocyclic molecules containing Sulphur linkage. Decomposed by acids, with the liberation of H 2 S. Characterized by thiozine ring, containing Sulphur atom. Some amorphous present in Sulphur dyes are as below:

9. Chemistry of Dyeing with Sulphur Dye: The Sulphur dyes contain Sulphur linkage within their molecules. They are insoluble in water but can be made soluble in water by treating them with reducing agents. This also makes them substantive towards cellulosic fibers. Na 2 S acts as reducing agent that breaks the Sulphur linkage and break down the longer molecules in to simple components which can penetrate the material (fiber/fabric) surface easily. This thios containing the –SH groups are readily oxidized by the action of atmospheric O2 or any other oxidizing agents. This reconverts the water soluble luco form of Sulphur dye in to previous water insoluble form which has a very good wash fastness property.

10. Sulphur dyes are negatively ionized. No Vander wall’s force effect on them is activated. Addition of salt improves efficiency of  dyeing  by increasing physical force. Chemical Structure: Sulphur dye contain Sulphur atom in their molecule and is characterized by the thiozine ring

11. A portion of Sulphur dye molecule is shown below: The structure formula is incomplete because the complete composition and structure of Sulphur dye is not known. Classification of Sulphur Dyes: Sulphur dyes may be classified in many ways. But according to their solubility there are essentially 3 classes of Sulphur dyes as below:- Conventional or Water insoluble dyes Leuco Sulphur dyes (Partially soluble) and Solubilised Sulphur dyes.

12. Oxidizing  Agent Reducing Agent Potassium Dichromate(K 2 Cr 2 O 7 ) Sodium Sulphide (Na 2 S) Acetic Acid(CH 3 COOH) Sodium Hydro sulphide (NaHSO 3 ) Sodium Perborate Thioglycolic acid Sodium per carborate Thio Salicylic acid Sodium peroxide (NaO 2 ) Pseudo thiohydantion Hydrozen peroxide (H 2 O 2 )

13. Conventional Sulphur dyes: (i.e. water insoluble Sulphur dyes) are dyed in following method. They have slight affinity to  textile fibers  of cellulosic origin. Method is as below:- Dye pasted with cold water ↓ Add required amount of Na- sulphide ↓ Dissolved by adding boiling water ↓ Boiled for 100 minutes to complete desolation ↓ Taken in dye bath containing soda ash ↓ Material immersed in dye bath ↓ Raising temperature & adding Glauber’s salt for exhaustion

14. Dyeing of Cellulosic Fibers with Sulphur Dyes: The sequence of dyeing with Sulphur dyes is as following: Goods Preparation ↓ Dye Solution preparation ↓ Dyeing ↓ Oxidation ↓ After treatment ↓ Dyed Goods

15. Typical Recipe: The Typical recipe for dyeing is as below:- Sulphur Dye                            :           10% (On the weight of the fabric) Na 2 S (Reducing Agent)         :           1.5% (On the weight of the Dye) Salt                                          :           8 gm/ litre ( NaCl ) Soda Ash (NaCO 3 )                :           7 gm/ litre Temperature                            :           100 C Time                                        :           90 minutes Material: Liquor                      :           1:20 Sometimes a chelating agent EDTA is added to chelate any metal salt extracted from the cotton goods & effectively remove these ions from the dye bath. This is necessary to prevent a harsh texture forming on a textile.

16. Good Preparation: Only normal pretreated fabric (scoured, bleached) is required. Mercerized cotton goods causes an increased colour yield of 30-40%, But goods bleached by Na-Hypochlorite should not be dyed by Sulphur dyes. Dye solution preparation or reducing step: Required amount of dye, soda ash & Na 2 S are taken in a beaker and a little amount of cold water is added to make a paste. In a separate vessel the rest of the water is boiled and the paste is added to it. Then the mixture is boiled for 5 minutes to make the dye completely reduced. Dyeing: At first dye solution is taken in a dye bath & the fabric is immersed in that solution. Then it is heated for 10-15 minutes. Then half of the total NaCl solution is added and temperature is raised to boil & then the rest amount of NaCl is added. Dyeing at this temperature is continued for about 30 minutes. Then the steaming is turned off and the application continued in cooling liquor for a further half hour. This steaming helps to diffuse the dye in to the fabric before fixing. Retained dye liquor should be rinsed out immediately from the surface of the fabric.

17. Oxidation: After dyeing the reduced water soluble form of the dye should be make insoluble by oxidation, to fix it on the fabric permanently. For this oxidation, we may use K 2 Cr 2 O 7 , CH 3 COOH. Na- perborate , Na 2 O 2  etc. The typical recipe of oxidation is as below: Na- Perborate                :        0.5-1 gm/ litre Temperature                :        40-50 C Time                            :        20 minutes. After Treatment: The dyed substance is soaped which makes the color bright and makes shade permanent. The light fastness property of Sulphur dyes which is generally good can be improved by after treatment with certain metallic salts. Thus a treatment with CuSO 4  & CH 3 COOH in presence of K 2 Cr 2 O 7  improves the  light fastness . When the dichromate is also present the washing fastness is slightly improved. The following recipe is used for after treatment: CuSO 4  Solution                      :        1-2% (on the weight of goods) CH 3 COOH (60%)                    :       1-2% Temperature                            :        70 C Time                                        :        20-30 Minutes

18. Precaution in the dyeing process: The precautions in the dyeing process with the Sulphur dyes are mentioned below: In the application of Sulphur dye, the dye bath should not contain Ca- Salts. If they are present in the form of insoluble co-compounds with the Sulphur dyes which precipitated easily in closed machines and form sludge when restrict the circulation of the dye liquor. The dye should be dissolved with soda. Great care should be taken during reduction process because over reduction should lower the affinity of dye towards the fiber. As a result dull shade will appear and a lot of dye stuff will go to waste. Fabric must not to expose to air during dyeing to prevent precipitation & oxidation. This will cause uneven dyeing. To prevent uneven dyeing in the fabric selvedge more amount of Na2S or NaOH and salt should be added in case of the  jigger dyeing machine . To prevent the broziness the dye liquor should not be very worm. Goods dyed with Sulphur black should be after treated with a solution of K 2 Cr 2 O 7  followed by rinsing. This will prevent Sulphur black tendering.

19. Control of Dyeing: Reduced Sulphur dyes are similar to direct dyes. Because they can also be exhausted by adding common salts ( NaCl ) or Glauber’s salt (Na 2 SO 4 .10H 2 O) to the dye bath. Sodium bi sulphite (NaHSO 3 ) and ammonium sulphate {(NH 4 ) 2 SO 4 } may also act as exhausting agents. Especially in dyeing combination shades. NaHSO 3  is an acidic salt and (NH 4 )2SO 4  is an acid liberating agent. They reduce the pH of dye bath and produce 15-20% deeper shades than common salt, when used as the exhausting agent. But the shades produced in presence of them are less bloomy and dull. When NaHSO 3  is used alone the rate of exhaustion is low but the produced shade is brighter and bloomier than common salt ( NaCl ) dyeing. The use of the exhausting agents causes wastage of dye but as the Sulphur dyes are relatively cheap this wastage is not considered. Especially in case of medium & light shades. Topping of Sulphur Dyes: Sulphur dyes act as mordents for the basic dyes. The cotton textile materials dyed with Sulphur dyes can be topped with basic dyes for brightening the shades. So, topping of Sulphur dyes is one kind of re dyeing by which required brighter shades are obtained. For topping of Sulphur dyes, at first dyed materials (dyed with Sulphur dyes) is washed thoroughly to remove the alkali from the fabric. Then the fabric is treated with basic dye in a second dye bath containing acetic acid of alum. In this bath temperature is raised about 60 C to control the exhaustion of basic dye.

20. Improving of Fastness Properties: The light fastness of the Sulphur dyes which is generally good can be improved by after treatment with certain metallic salts. Thus a treatment with CuSO 4  & CH 3 COOH in presence of K 2 Cr 2 O 7  or Na 2 Cr 2 O 7  improves the light fastness. When the dichromate is also present the washing fastness is slightly improved. In actual practice the following after treatments are given: – CuSO 4  Solution                      :        1-2% (on the weight of goods) CH 3 COOH (60%)                   :        1-2% Temperature                          :        70 C Time                                      :        20-30 Minutes The latter one also improves the washing fastness of Sulphur dyed textile materials.

21. Defects of Sulphur Dyeing: They are mainly two defects which are common in Sulphur dyed textile materials:- Bronziness or Dullness of shades Sulphur Black tendering Now they are Described below:- 1. Bronziness of Shades: This is a common defect found in Sulphur dyed textile materials. Causes: The causes are as below:- Excessive delay between lifting of the material from the dye bath and washing off. Exposure of goods to air while dyeing. Too much use of common salts as exhausting agents. Insufficient Na 2 S (i.e. reducing agent) in dye bath. As a result of which dye is incompletely reduced. Strong dye liquor in the dye bath.

22. Remedies: The remedies are as below:- Good washing and dilute solution of Na 2 S (0.1%) at 30 C or, A treatment with boiling soap solution or a strong  Na 2 S solution or, A treatment with a solution containing 10% salponified palm oil at 60 C or, Ammonia                    :           125-200 gm/100 litre or, 1.25-2 gm/ litre T.R Oil                         :           200-300gm/100litre or, 2-3 gm/ litre . Time                            :           15 minutes Temperature                :           Water Bath

23. 2. Sulphur Black Tendering: If Sulphur dyed textile materials are stored (weakening) tentering effect is seen on the cellulose. Due to storage a part of the Sulphur colour converts in to H 2 SO 4  by oxidizing which in turn causes degradation of cotton by hydrolysis. It is a serious problem of Sulphur dyed goods. Causes:  The causes are as below:- Gradual oxidation of Sulphur to H 2 SO 4  on storage. After treatment with copper salts causes rapid tendering. Presence of iron as an impurity causes rapid tendering. The method of oxidation for the recon version to insoluble form influence tendering. Remedies: The remedies are as below:- Treatment of dyed material with 1-3% K 2 Cr 2 O 7  and 1-3% CH 3 COOH at 60 C temperature for 30 minutes followed by through rinsing. Treatment with a little CH 3 COOH so that H 2 SO 4  may be converted in to harmless acetic acid. Using 5 gm/ litre soda ash after dyeing followed by drying without rinsing.

24. Stripping of Sulphur Dyes: Unevenly Dyed shades on cellulosic materials with Sulphur dyes may be corrected by a treatment with a worm solution of Na 2 S in the presence of Albigen A (polyvinyl pyrolodine ) If this method is found to be in effective then the uneven dyed material may be treated with a solution of a NaOCl or bleaching powder (2-3 gm/ Litre of available chlorine). In some cases bleaching with KMnO 4  solution may be effectively carried out. In other cases the dyed material may be treated with worm NaOCl solution in the presence of NaOH . The uneven dyeing of material causes due to the following reasons: The oxidation of dye during dyeing when the material comes in contact with air. Presence of gummy material on the fabric. Defective Dye. Uses of Sulphur Dye: To dye Umbrella cloth with Sulphur black. To dye cotton fabric e.g.-lining boot. To dye rubber material hence after treatment by CuSO 4  is necessary

25. S-Radical in Sulphur dye: In case of tendering of Sulphur , due to storage lose of strength occurs and forms to Sulphur radical. Three types of Sulphur radical are present in Sulphur dyes as below:- Mechanically free Sulphur : Air+S = H 2 SO 4 Stable Sulphur : 70%-80%, not easily oxidized. Chemically active Sulphur : 20-25% Colors/Shades found from Sulphur dyes: Red                             : Not good, not pure red color. Black, blue, brown      : Excellent Shade. Others                        : Olive, Orange, green etc. Causes for the Popularity of Producing Black Shades with Sulphur Dyes: Low cost Fair to good light fastness High Wash fastness Easy to apply Low energy required Chemical resistance is moderate to good. Wide range of shades especially on heavy, durable shades on apparel fabric.

26. Azo dyes and pigment

27. Azo dyes: The N=N group is called azo , related to AZOTE the French name of nitrogen . Azo compound are that bears the functional group R-N=NR , where R could be alkyl or aryl group . As a consequence of π - delocalization, aryl azo compound have vivid colors, especially reds, orange and yellow. They are used as dyes, and are commonly known as azo dye. Azo dyes and azo pigment are the most important class of both non metallized and metallized colorants. Azo compound coordinate with metal ions depend on the nature of the metal, their valence, type of chelating rings formation and pH of the reaction medium.

28. Azo Dyes used: Azo dyes have a variety of uses and are used by multiple industries. These are widely used in the pharmaceutical industry for adding color to medical types of equipment. These dyes play a major role in the cosmetic industry. The textile industry uses the Azo dyes to create different shades and add color to different materials and fabrics. These can be used as complexometric indicators as these undergo a color change in the presence of metal ions. Azo Dyes are used as medicine to treat insomnia. Thermal transfer printers also use the Azo dyes. Azo Dyes are great food colorants. Tartrazine is a lemon-yellow color azo dye used to add color to food.

29. Features of the Dye They possess a high fastness ability. These are used to dye the cellulosic material. Coupling these dyes is necessary for producing good colors. And coupling is done in an alkaline solution. It has admirable bright shades. The final color of the dye is produced after immersing the material for a few seconds. Therefore, it has a fast application. These dyes are suitable for small-scale industries. Azo Dyes  are effective and less expensive. The dye’s environmental impact is low, making it a safe option. It has a wide range of color options. These dyes are insoluble in water.

30. Why Azo Dye is so called? This color contains insoluble azo groups (– N=N –) in its chemical structure. That’s why this color is called Azo color. Azo Color Called ‘Ice’ and ‘Magic’ Color 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 NaNO 2  at ice temperature (0 – 5˚C). Magic Color Two steps are required by dyeing with azoic color. In the first step textile goods are dyed by Naphthol 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. 

31. Azo Dyes are Called ‘ Naphthol ’ and ‘Pigment’ Color Naphthol Color Azoic coupling components are insoluble in water. To make them soluble in water the  textile materials  are impregnated in a solution of Naphthol and NaOH . As the first coupling component is Naphthol color. Pigment Color Azoic dyes contain Azo group and final color is insoluble in water, so it is called Azoic Pigment. Base (Soluble)   +   Napthol (Soluble)  → Azoic dyes (Insoluble) Procedure for Dyeing Cellulosic Material Two bath of individual recipe is used for dyeing with azo dyes.      Impregnation Bath. Developing Bath. Impregnation Bath (1st bath) Recipe: 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)

32. . Developing Bath (2nd bath) Recipe 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% NaNO 2  → 1.5% Cold water → 10 times Temperature → 0˚C – 5˚C Time → 15 (2 – 3) minutes

33. Working Procedure Dissolve NaOH in small quantity of hot water with Naphthol & 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 Naphthol 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 naphtholate goods, excepting the naphthol 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 naphtholate 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.

34. Diazotization It is a chemical reaction where the fast base is to be converted to a solubilized form by the chemical reaction with NaNO 2  at ice temperature (0 – 5˚C).

35. Stripping Method of Azoic Color Stripping method of Azoic color: Recipe: NaOH → 4% (According to the wt of the material) Na 2 S 2 O 4  → 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 naphthol 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. Method 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. 

36. Precaution/Remarks in Dyeing with Azoic Dye Impregnation bath liquor can be preserved for a day or two days. Developing bath liquor cannot be preserved for a day. Naptholation material should never allow to come in contact with acid, alum and sunray. Generally 2 – 3 minutes duration is suitable for both impregnation and developing bath. If any way impregnating and developing liquor mixed together, the entire nature will be inactive and useless. 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. Bases yield comparatively better performance than salt.

37. Disperse Dyes :

38. The term “ disperse dye ” have been applied to the organic coloring substances which are free from ionizing groups, are of low water solubility and are suitable for dyeing hydrophobic fibres . The dye has derived its name for its insoluble aqueous properties and the need to apply it from an aqueous dispersion. Of all the dyes, they are of the smallest molecular size. Disperse dyes have substantivity for one or more hydrophobic fibres e.g. cellulose acetate, nylon, polyester, acrylic and other  synthetic fibres . Properties of Disperse Dyes Disperse dyes are nonionic dyes. So they are free from ionizing group. They are ready made dyes and are insoluble in water or have very low water solubility. They are organic coloring substances which are suitable for dyeing hydrophobic fibers. Disperse dyes are used for dyeing man made cellulose ester and synthetic fibers specially acetate and polyester fibers and sometimes nylon and  acrylic fibres . Carrier or dispersing agents are required for dyeing with disperse dyes. Disperse dyes have fair to good light fastness with rating about 4-5. The wash fastness of these dyes is moderate to good with rating about 3-4. Of all  dyestuffs  disperse dyes are of smallest molecular size. Generally disperse dyes are derivatives of azo , anthroquinone , nitro and quinine groups. They do not undergo any chemical change during dyeing.

39. Classification of Disperse Dyes A. According to Chemical Structure: According to chemical structure there are following types of disperse dyes: Nitro Dyes Amino Ketone dyes Anthraquinonoid dyes Mono azo dyes Di- azo dyes B. According to Fastness Property: According to fastness property there are following 4 types of disperse dyes: Group A: These dyes have excellent dyeing properties and good fastness properties. Group B: These dyes are excellent in high temperature and for carrier dyeing with moderate fastness. Group C: These dyes are moderate for carrier and high temperature dyeing with higher fastness property than group B dyes. Group D: These dyes are of excellent fastness to heat but for dyeing properties on carrier method.

40. C. According to Energy Requirement: According to energy required for dyeing there are following 3 types of disperse dyes: Low energy dyes: These dyes are used to dye with carrier. For dyeing 77°C temperature is required. They have extremely poor resistance to sublimation. Medium energy dyes: These dyes are used to dye mostly in between temperature 104°C-110°C which provides better sublimation fastness than that of low energy dyes. High energy dyes: These dyes are used to dye at temperature above 129°C and are suitable for continuous dyeing. They provide all round fastness properties. Chemical Groups in Disperse Dyes The percentage of chemical groups present in disperse dyes are as below: Mono azo dyes:                       50% Anthraquinonoid dyes:           25% Diazo dyes:                              10% Methyne dyes:                         03% Styryl dyes:                              03% Acrylene benzimidazol :          03% Quinonaphthalon dyes:          03% Amino naphthyl amide:          01% Napthoquinone imine :            01% Nitro disperse dyes:                01%

41. Name of dye Manufacturer Origin Foron Sandoz Switzerland Terasil Ciba-Geigy Switzerland Dispersol ICI UK Samaron Hoechst Germany SRA British Celanese Ltd. UK Setile ACNA Italy

42. Application Methods of Disperse Dyes Method N : Normal dyeing method. Dyeing temperature is 80-100°C. Normal NC method : Method of dyeing at normal temperature with carriers. Dyeing temperature 80-100°C. Method HT : High temperature dyeing method. Dyeing temperature 105-140°C. Method T : Thermosol dyeing method. Dyeing temperature 180-220°C, continuous method of dyeing. Pad roll method : Semi continuous dyeing method. Pad steam method : Continuous dyeing method. Factors Considered for Selection of a Method Availability of  dyeing machine . Required color effect (dark/medium/light). Required color fastness. Type of material to be dyed. Cost of dye, chemicals and auxiliaries. Overall economy of the system. Dyeing temperature.

43. Dyeing Mechanism of Disperse Dye The dyeing of hydrophobic fibers like polyester fibers with disperse dyes may be considered as a process of dye transfer from liquid solvent (water) to a solid organic solvent (fiber). Disperse dyes are added to water with a surface active agent to form an aqueous dispersion. The insolubility of disperse dyes enables them to leave the dye liquor as they are more substantive to the organic fiber than to the inorganic dye liquor. The application of heat to the dye liquor increases the energy of dye molecules and accelerates the dyeing of textile fibers. Heating of dye liquor swells the fiber to some extent and assists the dye to penetrate the fiber polymer system. Thus the dye molecule takes its place in the amorphous regions of the fiber. Once taking place within the fiber polymer system, the dye molecules are held by hydrogen bonds and Van Der Waals’ force.

44. The dyeing is considered to take place in the following simultaneous steps: Diffusion of dye in solid phase into water by breaking up into individual molecules. This diffusion depends on dispersibility and solubility of dyestuff and is aided by the presence of dispersing agents and increasing temperature. Adsorption of the dissolved dye from the solution onto the fiber surface. This dyestuff adsorption by fiber surface is influenced by the solubility of the dye in the dye bath and that in the fiber. Diffusion of the adsorbed dye from the fiber surface into the interior of the fiber substance towards the centre. In normal condition, the adsorption rate is always higher than the diffusion rate. And this is the governing step of dyeing.

45. Dispersing Agent Disperse dyes are insoluble in water and form aqueous dispersion in water. At first these dye molecules are formed as large particles and they are made smaller particles by grinding. But as they are water insoluble, they will give uneven dyeing if they are directly used in dye bath. So to ensure uniform and trouble free dyeing the dye should be present in dye bath in an uniform and very fine form and should give an stable dispersion. This is the reason for which a special chemical is used in dye bath named dispersing agent. They should be effective under dyeing conditions, stable to hard water, high temperature and other dyeing assistants. For example, soap powder, Turkey Red oil, alkali sulphates , alkyl aryl sulphonates etc. are some surface active agents which are recommended as dispersing agents in disperse dyeing. Functions of Dispersing Agent It assists in the process of particle size reduction of dye. It enables the dye to be formed in powder form. It facilitates the recon version of the powder into a dispersion which is required for dyeing. It maintains the dispersion in a fine form in the dye bath through out the process. It increases the solubility of disperse dyes in water. It affects on the art of dyeing.

46. Heat Setting Procedure of Polyester Fabric The process of  heat setting  is used to stabilize yarn twist, remove residual shrinkage, increase wrinkle resistance and obtain durable pleat. Polyester may shrink 7% at boil and even more at higher temperature. The importance of heat setting is as below: To modify crystalline structure. To improve dimensional stability. To resist wet creasing during washing. To increase safe ironing temperature. To avoid shade variation. Affect water inhibition. The disadvantages of heat setting are: Some dyes sublime at high temperature. Pre setting reduces dye uptake.

47. Reduction Cleaning In case of dark shade dyeing, we have to use more amounts of dye and chemicals. But these chemicals should be removed from fabric after dyeing. For this reason, a special process is used in case of disperse dyeing. This cleaning process is called reduction cleaning. A typical recipe for reduction cleaning is given below: 1 gm/lit:                        Tingal W 2 gm/lit:                        Hydrosulphite 2-3 ml/lit:                     NaOH (56.5° Tw ) By reduction cleaning, surface dye molecules or unfixed dye molecules are stripped and this in turn results in level dyeing. Reduction cleaning also improves  wash fastness  property of textile material. Carriers It has been established that certain hydrocarbons, phenols, amino acids, amides, alcohols, esters, ketones , nitriles etc. accelerate the rate of dyeing polyester fiber with disperse dyes from aqueous medium at temperature up to 100°C. These dyeing assistants alter the dispersing properties of the dyes and the physical characteristics of the fiber so that more dye can be transferred from the dye bath to the fiber. These are called carriers and are necessary for dyeing polyester fibers at the normal pressure and temperature below 100°C to increase the dyeing rate and to permit dye migration within the fiber. Level dyeing of disperse dyes depend on the migration power of the dye which is affected by nature and amount of carrier, dyeing time, temperature and the shade.

48. Commercial Name Manufacturer Chemical Class Solvent OP Franco O-phenyl phenol Tumescal D ICI Diphenyl Palanil Carrier A BASF Aromatic Ether Carrier PDC TCC Emulsifiable solvents Dilatin TCR Sandoz Chlorinated aromatic compound Butyl oleate HAR Ester Some Commercial Carriers

49. Factors Considered for Selecting a Carrier High carrier efficiency. Availability at low cost. Little or no effect on light fastness of final dyeing. Absence of unpleasant odor. Non toxicity. No degradation or discoloration of fiber. Ease of removal after dyeing. High stability under dyeing conditions. Compatibility with dyestuffs. Ease of dispersion in the dye bath. Low volatility of the carrier including low volatility in the steam. Uniform absorption by the fiber.

50. Dyeing of Polyester Fabric with Disperse Dye in Carrier Method The extreme crystalline nature of polyester fibers creates problems in obtaining dark shades by conventional dyeing methods even at high temperature. The carriers are found to assist the disperse dyes to enter the polyester polymer, enabling dark shades to be produced. The carriers swell the polyester fibers, increase inter polymer space and let the dye molecules to enter the polymer system easily. RECIPE: Dye – For light shade<0.5% – For medium shade 0.5-1.5% – For deep shade>1.5% Carrier (phenol)           : 3gm/lit Acetic acid                  : 1gm/lit Dispersing agent         : 2gm/lit Salt (NH 4 ) 2 SO 4          : 1-2gm/lit pH                               : 4-5.5 M:L                             : 1:10 Time                            : 60 min Temperature                : 90°C

51. PROCEDURE: At first, a paste of dye and dispersing agent is prepared and then water is added to it. Dye bath is kept at 60°C temperature and all the chemicals along with the material are added to it. Then the bath is kept for 15 min without raising the temperature. pH of bath is controlled by acetic acid at 4-5.5. Now temperature of dye bath is raised to 90°C and at that temperature the bath is kept for 60 min. Then temperature is lowered to 60°C and resist and reduction cleaning is done if required. Reduction cleaning is done only to improve the wash fastness. Material is again rinsed well after reduction cleaning and then dried.

52. Advantages of Carrier Dyeing In conventional dyeing method, the extremely crystalline polyester fibres can not be dyed in deep shade. But by using carrier we can get medium to dark shade in boiling temperature. Materials can be dyed with simple equipments at atmospheric pressure and temperature below 100°C. Moderate level dyeing of polyester fabric can be done. Some carriers reduce the staining of wool while dyeing polyester-wool blends. Rate of dyeing can be increased by using carriers. Can be dyed quickly by using carriers. Improves fastness properties of fabric except light fastness. Disadvantages of Carrier Dyeing Carriers add to production cost of dyeing. Firstly, for dyeing it is used which is costly and secondly for its removal alkali is required. Carriers are unhygienic and toxic. It creates skin diseases. Some dyeing machines may create carrier spot. Carriers affect the light fastness property of dyed material. This effect may be reduced by treating the material with hot air for 30 min. Some carriers are dyed specific. They posses different efficiencies with different dyes; others have compatibility with certain dyes.

53. HIGH TEMPERATURE DYEING METHOD: Dyeing of Polyester Fabric in High Temp Dyeing Method In high temperature dyeing method either material or liquor should circulate. Otherwise dye molecules will not penetrate inside the material. They will stay on surface only. In this method, temperature is kept in between 105-140°C and pressure is kept from 0 to 170 kPa . This method is also known as pressure dyeing which is used for highly crystalline synthetic fibers and their blends. This technique causes the fiber to swell even more than which achieved at 100°C temperature. So that dye molecules penetrate the fiber polymer system. It eliminates the need of carriers. RECIPE: Dye                              : 3% Dispersing agent        : 1gm/lit Acetic acid                  : 1gm/lit Time                            : 60 min Temperature               : 130°C pH                               : 4-5.5 M:L                             : 1:10

54. PROCEDURE: At first a paste of dye and dispersing agent is prepared and water is added to it. PH is controlled by adding acetic acid. This condition is kept for 15 minutes at temperature 60°C. Then the dye bath temperature is raised to 130°C and this temperature is maintained for 1 hour. Within this time, dye is diffused in dye bath, adsorbed by the fiber and thus required shade is obtained. The dye bath is cooled as early as possible after dyeing at 60°C. The fabric is hot rinsed and reduction cleaning is done if required. Then the fabric is finally rinsed and dried.

55. Super Heated Steaming: The features of this method of dye fixation are mentioned below:- It is a continuous process of dye fixation. This method is the best of the three methods. Dye is fixed at 100 -180 C for 2-1 minutes by radiators. Higher productivity. No loss of colour . Dyes with medium sublimation fastness can be applied. The fabric handle is very soft. High Pressure Steaming: The features of this method of dye fixation are mentioned below:- Discontinuous process of dye fixation Low productivity. Dye fixation is done by high pressure steam. Low production so costly process. Dyes with low sublimation fastness can be applied. It gives good Color yield and bright print & smoothness.

56. Reduction Cleaning: After the fabric is applied dye fixation method it is subjected to reduction cleaning process. Reduction cleaning process is carried out for obtaining deep shade (>5%-15%) For reduction cleaning a bath is prepared containing:- Caustic Soda                :           2 gm/ litre Hydrosulphite               :           2 gm/ litre Na-ionic Datergent        :           2 gm/ litre M : L Ratio                     :           1:5 Time                            :           30 Minutes In the bath caustic soda and Hyd - rosulphite are taken for the stripping of dye and non-ionic detergents is taken for washing off. After passing the printed fabric through this bath then the fabric is washed off, by hot air & then with cold water.

57. Thanks to all