The document discusses vat dyes, which are insoluble aromatic compounds containing quinone groups. Vat dyes are reduced to a soluble hydroquinone form using reducing agents like sodium dithionite and sodium hydroxide for application to cellulosic fibers. The reduced dyes are then oxidized back to the insoluble pigment form within the fibers. Vat dyes provide excellent fastness properties and can withstand various treatments. Common application methods include reduced vat dyeing in jigs or stock vats, and continuous padding and developing processes. Post-dyeing treatments may include oxidation, soaping, leveling, or partial stripping to correct any faults.

1. VAT DYES Except Deep Red 7/2/2008 1

2. Introduction 1 Chemical Structure of Vat Dyes 2 Dyeing Structure of Vat Dyes Treatments After Exhaustion of Vat Dyes Semi and Fully Continuous Method 3 5 6 Method of Dyeing 4 Overview 7/2/2008 2

3. Wet on Wet Process 7 Fixation Process 8 Package Dyeing Correction of Faulty Dyeing Indigo Dyeing for Denim Solublised VAT Dyes 9 11 12 13 Dyeing of Knit Goods 10 Overview 7/2/2008 3

5. All of these dyes have good fastness against

6. Wet treatments

7. Crocking

8. Light fastness in the region of 6 to 7.

9. The vat dyes can also withstand oxidizing agents like

10. Hydrogen peroxide (H202)

11. Sodium Chloride (NaCl)

12. Hypochlorite (--OCl)7/2/2008 4

14. THIS CLOTH can undergo the pretreatment processes like

15. Alkali Boiling

16. Bleaching

18. Because reactive dyes less expensive , easier to apply.

19. Vat dyes are still popular on account of the all round high fastness properties.

20. VAT DYES ARE COMMONLY USED FOR:

21. Superior Quality Shirting Material

22. Military Uniforms

23. Furnishings, Curtain, Toweling etc.7/2/2008 5

25. That cover the entire Gamut(range) of shades except Deep Red Colors.

26. VAT DYES ARE ESSENTIALLY Insoluble Polycyclic Aromatic Compound:

27. Containing Two or more pair of QUINONE GROUPS

28. Indigo and Tyrian Purple belongs to this family.

29. VATTING: In order to apply cellulosic Fibers

30. VAT PIGMENTS are made water soluble by reducing to HYDROQUINONE Forms in an alkaline media.This process Known as Vatting.

31. Vatting Term referring to a historical link with the vegetable Indigo Dye that used to reduced in WOODEN VATS with natural reducing agents like sugar.

32. PRESENT VATTTING CHEMICALS ARE:

33. Sodium Hydroxide

34. Sodium Dithionate(Na2 S2 O4) a strong reducing agent one with high reduction potential. Commonly termed in Industry as Sodium Hydro Sulphite or Simply HYDROS.

35. Sodium Dithionate reduces the KETO GROUPS into the ENOL Form

36. Sodium Hydroxide forms sodium salts of the ENOL to make the DYES WATER SOLUBLE.7/2/2008 6

38. Sodium Hydroxide

39. Sodium Dithionate(Na2 S2 O4) a strong reducing agent one with high reduction potential.

40. Commonly termed in Industry as Sodium Hydro Sulphite or Simply HYDROS.

41. Sodium Dithionate reduces the KETO GROUPS into the ENOL Form

42. Sodium Hydroxide forms sodium salts of the ENOL to make the DYES WATER SOLUBLE.

43. Caustic Soda Also NEUTRALISE THE ACIDIC Decomposition products of the reducing agent ‘DITHIONITE’ produced during vatting and Dyeing.7/2/2008 7

45. Quantity of Reducing Agent Depend upon

46. No. of KETO groups Present in the Dye Molecule

47. To the extent/ amount of exposure or the dye bath to AIR.

48. Reduction is Accompanied by

49. Change in Color that is due to alteration in the conjugation of DOUBLE BONDS.

50. The reduced indigo has a PALE SHADE and so it was called the LEUCO(white) dye.7/2/2008 8

52. accidently prepared a blue dye from ANTHRAscene, which he named as an INDANthrene dye. Soon after this breakthrough

53. Bohn and his Coworkers synthesize many other VAT DYES.

54. THE VAT DYES ARE OFTEN CLASSIFIED AS:7/2/2008 9

56. Direct dyes

57. As for as adsorption on the cellulose fibres is concerned

58. But the ANTHRAquinone derivatives have

59. High intrinsic substantivity

60. In spite of lack of linearity and

61. Hydrogen bonding groups attributed

62. to the molecular complexity

63. And CO-PLANARITY of the VAT dyes.

64. As a High Concentration of SODIUM IONS from Caustic Soda(NaoH) and Sodium Dithionate(Na2 S2O4)

65. Already exist in the Reduced Bath.

66. The VAT dye tend to have HIGH RATE of adsorption

67. And EXHAUSTION in the initial stage of Application.

68. The RAPID ADSORPTION of dye in the first few minutes:

69. Technically termed as “HIGH STRIKE” value.

70. This tendency require a careful attention as well as ADDITION of RETADING agents to obtained level dyeing.7/2/2008 10

72. AN OXIDIZING AGENT IS ADDED TO THE BATH

73. That regenerates the VAT PIGMENT inside the fibres.

74. Finally, to achieve full fastness properties and to develop the proper shade, the dyed goods are

75. THOROUGHLY SOAPED AT BOIL.

76. VAT dyes three main classes for APPLICATION PUPOSES.7/2/2008 11

78. In their Leuco forms Have High substantively for the cellulosic fibres.

79. These needs High Alkalinity for Dissolution

80. And are dyed at about 75o c.

81. Where I stands for Indanthrene and W for Warm

82. In their MODERATE substantivity for cellulosic fibres.

83. These needs MEDIUM Alkalinity for Dissolution

84. And are dyed at about 45o c TO 75o c.

86. Have LOW substantivity for the cellulosic fibres.

87. These needs moderate Alkalinity for Dissolution

88. And are dyed at low temperature about 20o c to 30o c..

89. Needs in a Higher concentration Electrolytes than class II for complete EXHAUSTION of the dye.

90. Dyes of the IK Group other than the Indigo, are Not much used now a days.

92. Reduced in a JIGGER.

93. For continuous processes,

94. Fabric is PADDED in stable dispersion of very finely divided vat pigments often termed as MICRO-DISPERSIONS.

95. After drying the dye padded fabric, it is reacted with an ALKALINE REDUCING SOLUTION in a padder to VAT PIGMENT into water-soluble LEUCO FORM

96. LEUCO FORM diffuses into the fibre.7/2/2008 14

98. This process is applicable for

99. Batch wise dyeing WOVEN and KNIT fabrics

100. Also for YARNs in hank or package form.

101. REDUCTION OF the dye is faster in the STOCK VAT

102. BECAUSE

103. Concentration of the dye and reducing chemicals is higher than LONG BATH.7/2/2008 15 The dye is first reduced into SOLUBLE FORM. In the bath(long liquor) Or in the stock vat Before bringing it in contact with substrate

105. THE MORE Difficult to reduced CLASS I dyes:

106. Vatted by the STOCK VAT method.

107. This dispersion at optimum temperature

108. Stirred for 10 minutes. When reduction is COMPLETE.

109. SOFT WATER must for dissolving and as far as dyeing.

110. Dyeing in HARD WATER causes precipitation (useless product) COUNTER THIS PROBLEM by use of SQUEStering AGENT.7/2/2008 16 Dye is pasted with the dispersing agent. And soft water And then the required quantities of Caustic Soda(NaoH) And DI-THIONATE(S2O4) Are added as per manufacturer literature.

111. METHOD DYEING REDUCED VAT DYEING: 4 7/2/2008 17

113. GENERAL IDEA OF CONCENTRATION

114. OF rducing and exhausationchemicalsrequired in the bath at a liquor ratio of 10:17/2/2008 18

116. a nonionic retarding agent (ALKO-Xylated type)

117. Is often added that forms a complex with the REDUCED dye and release it gradually as the bath is exhausted,

118. addition of the Retarding or LEVELLING agent is more necessary

119. When dyeing mercerized COTTON, Regenerated RAYON

120. And for PALE SHADES

121. And also in LOW LIQUOR ratios.

122. These LEVELLING Agent reduce the ultimate dye- uptake slightly,7/2/2008 19

123. METHOD DYEING REDUCED VAT DYEING 4 7/2/2008 20

125. OVER – REDUCED

126. Their SHADES becomes LIGHTER or even ALTERED.7/2/2008 21

128. Dyes of IN and IW groups temperature

129. can be raised to 80o C

130. The Dyeing Continued for 45 TO 60 minutes.

132. And dyeing is carried out in a cooling BATH after attaining TEMP of 45o C.

133. However SPECIAL REDUCING AGENTS of the HYDROXY-Alkyl-Sulphinate type may have to be used that can withstand decomposition at these HIGH Temperature.7/2/2008 22

134. TREATMENTS AFTER EXHAUSTION OF DYES 5 AFTER EXHAUSTION OF THE VAT DYES 7/2/2008 23

135. TREATMENTS AFTER EXHAUSTION OF DYES 5 AFTER EXHAUSTION OF THE VAT DYES 7/2/2008 24

136. TREATMENTS AFTER EXHAUSTION OF DYES 5 AFTER EXHAUSTION OF THE VAT DYES 7/2/2008 25

137. TREATMENTS AFTER EXHAUSTION OF DYES 5 AFTER EXHAUSTION OF THE VAT DYES 7/2/2008 26

138. TREATMENTS AFTER EXHAUSTION OF DYES 5 AFTER EXHAUSTION OF THE VAT DYES 7/2/2008 27

140. With a very fine dispersion (PARTICLE SIZE 0.5 – 1 um) of VAT PIGMENT.

141. Then to convert the absorb pigment into LUECO FORM

142. This is followed by

143. OXIDATION

144. SOAPING in a Washing Range

145. The MAIN ADVANTAGE of this process over the reduced-VAT method are as under.

146. A) HIGH PRODUCTIVITY

147. B) BETTER LEVELLING

148. C) GOOD PENETRATION7/2/2008 28

150. a wetting agent.

151. The latter is added for quick wetting of the fabric.7/2/2008 29

153. HOT FLUE or

154. CYLINDER DRYER

155. Incase the cylinder are used

156. The IR-predryer is must

157. First few cylinder Teflon Coated as to reduce staining.

158. Temp 100oC first few cylinders to minimize Migration and two sided effect.7/2/2008 30

160. In the BATCH PROCESS

161. Reduction and

163. Alkali and Reducing Agent

164. IF variation in SHADE due to BLEEDING in not totally eliminated

165. In the CHEMICAL PADDER 5 – 10 % of the bath is made with the pad liquor7/2/2008 31

166. Semi and Fully Continuous Dyeing Method 6 Different steps involve in the APPLICATION are: 3. DEVELOPMENT: CONTINUOUS PROCESS 7/2/2008 32

167. 7/2/2008 33 Semi and Fully Continuous Dyeing Method 6 OXIDATION AND SOAPING In the Continuous Process, In a WASHING RANGE In which fabric is treated in the following different sequences:

168. 7/2/2008 34 CORRECTION OF FAULTY DEING 7 Fauls are usually corrected by Levelling Out Partial Stripping or Cross Dyeing However kept in mind LEUCO VATS have a very high affinity with cotton fibers and so difficult to strip off the dyed goods.