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Introduction to dyeing


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Introduction to dyeing

  2. 2. Basic Textile Terms and DefinitionsDyestuff is organic or inorganic substanceswhich can absorb light and reflect some lightsto show color. Actually, the dyestuff is watersoluble substances.Pigment is a substance that can absorb lightand reflect some lights to show color but it iswater insoluble substances. Normally it isused for printing (with the presence of binder)or mass-coloration of the synthetic fibers. 2
  3. 3. Staining is an unpleasant of dyeing in thearea that we do not want.Exhaustion of the dyestuff to the fibers is asfollows:1. Moving of dyestuff from dyebath tosurface of the fiber2. Adsorption of the dyestuff into the surfaceof the fiber3. Diffusion of the dyestuff into the center ofthe fiber 3
  4. 4. Classification of DyestuffsDyestuffs can be classified by many methodsas follows:1. by their ionic (e.g. cationic, anionic andnon-ionic)2. by their fiber dyeabilities (e.g. oncellulosic, protein, polyester, polyamide etc.)3. by their names (e.g. acid, direct, disperse,reactive, basic etc.)4. by their chemical structures (e.g. azo,anthraquinone, stilbene etc.)5. by their origins (e.g. natural, synthetic)6. by their colors (e.g. red, green, black etc.) 4
  5. 5. Dyeing Processes can be applied in manystages such as1. Mass-coloration of the molten fibersThis method is for dyeing the moltenfibers or plastic chips or textile polymerswith pigment dyes. After that, the moltenor polymers will extrude from a spinneretto form fibers.Normally, the synthetic fibers are addedwith white pigment in order to give ahiding power (non-see through fabrics).Advantage: give excellent fastnessDisadvantage: very difficult to clean 5
  6. 6. 2. Fiber Dyeing is the method of dyeingfibers before blending with other colors togive fancy yarns or fabrics.Note: This is used for special purposes only.3. Yarn Dyeing is the method of dyeing yarnsin forms of hanks or packages dyeing. Thiswill give Scottish’s style fabrics, carpet withmany colors and styles.Note: This is used in hand loom weaving inthe Northern and North-eastern parts ofThailand. 6
  7. 7. 4. Fabric Dyeing is the method afterweaving, knitting, or non-woven to makefabrics. This is very popular method ofdyeing as the dyed fabrics will be processedfurther to garment industries very easily.Dyeing forms of the fabric dyeing can beused in 2 ways:1. Open width form using the fabrics tospread without any creases and dye them.2. Rope form using the fabrics with theform like a rope (many creases and looklike “a rope”) 7
  8. 8. Some people classify into: 1. Exhaustion Process This method is using lot of water as shown in “Liquor Ratio (ratio between water and goods)” This should immerge the goods into dye solution for a long time in order to let the dye penetrate into the goods. This will lead to produce more waste water than the continuous process.Advantage: inexpensive, no need to train theworker to look after and run them properly.Disadvantage: lots of water needed, veryslow process (60-120 min/batch.) 8
  9. 9. 2. Continuous ProcessThis method is designed by putting differentmachinery into a sequence so that it canproduce the dyed fabric in one pass.Advantage: very fast process (10-100m/min), small amount of water in theprocess.Disadvantage: very expensive, need to trainthe worker to look after and run themproperly. 9
  10. 10. 6. Garment DyeingThis method is the last process of thedyeing of goods. However, the penetrationof the dye solution may not be completelypassed to the fibers such as between theseams, buttons, zippers etc. Normally, it isused for lingerie, socks, sweater dyeing etc. 10
  11. 11. Name of Dyestuffs Fibers that can be dyedAcid Silk, wool, polyamide, leatherBasic AcrylicDirect Cellulosic, viscoseDisperse Acetate, triacetate, polyamide, polyester, acrylicReactive Cellulosic, viscose, proteinVat CellulosicSulphur Cellulosic 11
  12. 12. Factors that give some choices of thedyestuffs1. Cheap2. Non-toxic3. Compatible to other dyes and chemicals4. High color strength5. Better brightness6. Better fastness7. Good levelness on the materials 12
  13. 13. Dyes for Cellulosic Fibers Direct Dyes (Anionic)They can be dyed directly on cellulosicfibers. Without the presence of salt, whenthe fibers are immerged in water, it will showanionic charge which repels the dyes.Adding salt into the dye bath, it will reduceanionic on the fibers so the dyes can getcloser and adsorb into the fibers.Advantage: cheap, easily dyed on fibersDisadvantage: poor wet fastness and somedyes have poor light fastness. 13
  14. 14. Textile Auxiliaries1. Salt - reduce negative charges on thefibers2. Water - dyeing media3. Fixing Agent - enhance wet fastness butusually reduce light fastnessDyeing Conditions (Exhaustion)dyeing 100oC x 30-90 minfixing 60oC x 20 min(Continuous)pad --> dry --> steam --> wash --> soap --> 14dry
  15. 15. Reactive Dyes (Anionic)They can be dyed on cellulosic fibers. Themechanism is nearly the same as described inDirect dyes.Advantage: high wet fastness due to covalentbonding (Chemical Bonding) between fibersand dyes, easily dyed on fibersDisadvantage: Expensive 15
  16. 16. Dyeing Conditions1. Continuous Process1.1 Pad-dry-bakeThis is very easy method for cotton or cottonblends fibers.1.2 Pad-dry-Pad (Chemical)-SteamThis will give brighter and more intensecolor than method Pad-batchThis will put the goods into the dye solutionand squeeze with 2 rubber rollers to get rid ofexcess water and then batch at roomtemperature for 1-2 days. 16
  17. 17. 2. Exhaustion ProcessThis method will be used in small factory.Dyeing conditions will be 40-80oC for 30-90min depending to the types and structures ofthe dyes. 17
  18. 18. Textile Auxilaries1. Salt - reduce negative charges on thefibers2. Water - dyeing media3. Soda Ash - excite the dye to link with thefibers with covalent bonding. Therefore, itenhances wet fastness4. Fixing Agent - enhance wet fastness forheavy shade but usually reduce light fastness. 18
  19. 19. Vat Dye (Anionic when soluble)The dye is named from the container (Vat)that used for rotting the dye with alkalisolution. This crucial process will reduce thedye from insoluble to soluble dye (suitablefor exhaustion in the cellulosic fibers). Nowthe manufacturer can synthesize man-madevat dye. 19
  20. 20. Dyeing Process1. Dissolve dye into water (insoluble dye)2. Vatting process by reducing the insolubledye in alkali condition. (soluble dye)3. Absorb into fibers (soluble dye)4. After dyeing, oxidize the dye withoxidizing agent (insoluble dye)5. Wash and soap the goods 20
  21. 21. Dyeing Conditions1. Continuous Process1.1 Pad-dry-Pad (Chemical)The solution of the dye is prepared withoutadding reducing agent to ensure levelingdyeing. After that, the goods are passed tochemical bath to reduce the dye into solubledye and fix within the goods. Oxidizingagent is added to the goods and converted toinsoluble dyes. 21
  22. 22. 1.2 Pad-oxidize-pad-oxidize (many times)This will put the goods into the dye solutionand squeeze with 2 rubber rollers to get rid ofexcess water, oxidize with the air and thenimmerse into the dye solution again andagain to allow the dye penetrate into thegoods. 22
  23. 23. Textile Auxilaries1. Salt - reduce the negative charges on thefibers2. Sodium hydroxide - adjust pH to thedyeing bath and make the suitable conditionsfor reducing agent.3. Sodium hydrosulfite - reducing agent forthe vat dyes.4. Water - dyeing media5. Oxidizing agents - (Hydrogen peroxide orAcetic acid or Air) oxidize the soluble toinsoluble dye 23
  24. 24. Sulfur Dye (Anionic when soluble)The dyeing process has the same process asdescribed in the vat dye except that usingSodium sulfide instead of Sodiumhydrosulfide. 24
  25. 25. Dyes for Synthetic Fiber Disperse Dye (polyester, nylon, and acetate) (non-ionic)The dye is named from less water solubleand normally appeared in dispersion in water.The dye shows no charge due to the groupspresented in the dye molecules. Dyeing Conditions Insoluble Less water Water insoluble dye in soluble in polyester water fibers 25
  26. 26. 1. Exhaustion Process1.1 At boil with carrierThis process is suitable for acetate fiber andpale shade polyester fiber dyeing. Carrier isan auxiliary for swollen fiber in order toallow more dyes absorbing in. Now the useof carrier is reduced because it may be acarcinogen.1.2 At 130oC without carrierWith the high temperature, the dyes will bedissolved into smaller molecules and the voidin fiber structure will be opened. This willgive heavy shade. 26
  27. 27. 2. Continuous ProcessPad --> Pre-dry (100oC x 30 sec) -->Thermofixation (180oC x 30 sec) -->reduction clearing (RC) --> wash --> dry Printing with Disperse DyesWith the sublimation property, the dyes canbe printed on paper, place the fabric with aprinted paper and then using an iron withhigh temperature pressed on the paper. Thedyes will transfer from paper to polyesterfiber. This is called “Transfer Printing”. 27
  28. 28. Textile Auxilaries1. Dispersing Agent - make the dye solutionstable and disperse in the dye bath.2. Acid - adjust pH to the suitable conditionfor the dye bath.3. Carrier - swell the fiber and dissolve thedye to make the dye getting into fiber.4. Leveling agent - make more levelingdyeing (some will have adverse effect onslower dyeing)5. Water - dyeing media 28
  29. 29. Reduction Clearing (R.C.)After dyeing process, the dyed goods shouldbe removed excess dyes on the fiber surface.R.C. will give higher washing and rubbingfastness of the dyed goods.Using alkali solution, sodium hydrosulfideand dispersing agent, the R.C. will be done at60oC x 20 min.Note: Do not use more than therecommended temperature because sodiumhydrosulfide can be decomposed. 29
  30. 30. Acid Dye (Anionic)The dye is called acid because it needs acidicdyeing condition. It can be dyed on proteinfibers (silk, wool, other animal fibers) and onpolyamide fibers.Acidic condition will give the fibers showingpositive charge. As the negative charge willattach directly to positive charge, andpenetrate into the fibers. Dyeing conditions100oC x 30-60 min 30
  31. 31. Textile Auxiliaries1. Leveling agent - for levelness dyeing2. Retarding agent - for inhibiting the dye notattach to fibers too fast3. Acid - adjust the dyeing condition andmake the fibers to show positive charges4. Water - dyeing media 31
  32. 32. Basic Dye (Cationic)The dye shows positive charge. Normally,the dye can be applied on wool, silk andpolyacrylonitrile (acrylic). Dyeing Conditions100oC x 30-60 min 32
  33. 33. Textile Auxiliaries1. Leveling agent - for levelness dyeing2. Retarding agent - for inhibiting the dye notattach to fibers too fast3. Acid - adjust the dyeing condition andmake the fibers to show negative charges4. Water - dyeing media 33
  34. 34. Dyes Dyeing Condition (pH)Acid (Wool) 2-4, 4-6, 6-8 (depends on types of dyes)Acid (Nylon) 4.5-5.5, 6-7 (depends on types of dyes)Basic 3.5-4Direct 7.0Disperse (Polyester) 5-6Disperse (Acetate) 6.5-7.0Disperse (Triacetate) 4.5-6.5Reactive 7.0 (Exhaustion) 11.0 (Fixing) 34 -------------------------