DYEING OF POLYESTER BLENDS Limited manufacture in India Most popular blend :55/45 PET/Wool Other blend ratios : 70/30, 20/80 55:45 blend –warp and weft blended yarn Polyester Rich Blend: 70/30 (textured 100% PET warp & 55:45 blended weft) Wool Rich Blend : 20/80 (with 55:45 blended weft and 100% wool weft)

PRETREATMENT: Typical process sequence: 1)Grey inspection 3)Scouring 5)Dry 7)Dye 9)Singeing 11)Decatising and Pressing 2)Stain removal 4)Wool presetting(crabbing) 6)Heat set 8)Brushing, Cropping 10)Steam or Damp Other sequences page 239

SCOURING: Remove spin finish, lubricating agent, natural waxes, size, other contaminants Fabric relaxation Anionic or non-ionic detergents are used Use of alkali like soda ash should be avoided Rope form e.g. Dolly washing machine for wool rich or 55:45 blends Open width e.g. for polyester rich blends

Non-ionic Detergent scouring: Brief scouring at 10 0 C above cloud point of detergent –helps to form detergent-oil complex. Drain to remove surface impurities Scour 30 – 45 min. at 5 0 C below the cloud point of detergent.

Crabbing: For setting wool component Basically hot water treatment carried out in open width. Temp.: ~ boil, for 30 – 45 min. Does not have lasting effect due to heat setting on PET –may be necessary to repeat crabbing to smoothout creases Second crabbing –at 60 0 C Dried on stenter at C.

Heat setting Normally done before dyeing Important variables: Time, Temperature, Distinct phases: * fabric setting up phase * heat penetration phase * molecular orientation phase * cooling phase

Fabric heating up phase: To raise the fabric surface temperature to the required value say 180+/-10 0 C. Time required depends on * fabric structure * rate of heating * thermal conductivity of the fabric (15 sec. for low conductivity fabric)

Heat Penetration and Molecular Orientation Phase: quickest – 5 sec. Cooling Phase : stabilization of relaxed polymer structure - ~ 10 sec. Total heat setting time - ~30 sec.

Heat setting stage: Grey heat setting After scouring

Grey heat setting: Merits Stiffness imparted is removed during subsequent scouring Less chance of tendering due to absence of alkali left during scouring Easy to handle Demerits Oil stains and size are fixed -skittery appearance of dyed fabric

Heat setting after scouring: Merits Clean operation Fabric appearance is bright Oils and other materials are not fixed –faultless dyeing Demerits Stiff handle –may be light fabric is needed If alkali is left in fabric –damage of wool, yellowing.

Dyeing G eneral considerations: HTHP at C-damage to wool component Heavy staining of wool with disperse dyes – poor fastness properties –should be avoided High temperature and prolonged dyeing time –less staining, wool damage Lower temperature and shorter dyeing time are preferred.

Dyeing conditions: At boil with carrier At C with addition of smaller amount of carrier compared to at boil C with the addition of formaldehyde as wool protecting agent, a small amount of carrier if necessary

Dyeing methods One bath method : * simultaneous dyeing of PET and wool with disperse and wool dyes * common method for pale and medium depths of shade * economical, * minimum tendering of wool Two bath method: * mainly for navy and black shades * no particular advantage over one-bath method

Staining of wool: Less in prolonged dyeing –but chance of wool tendering More rapid exhaustion of disperse dye on PET –less staining of wool Fine wool fibres are stained more severely than coarse wool fibres

Dyebath Auxiliaries: Dispersing agent Antifoam agent Carrier Crease inhibitor Levelling agent for wool dyeing Wool protecting agent

Carrier The choice depends on the machinery used: Closed machinery Fully flooded Partly flooded Covered machines Open machines Carrier -Very volatile carriers % volatility e.g.dichloro & trichloro benzene -Medium to low volatality (40 – 70%) e.g.mixture of i)biphenyl /trichlorobenzene ii)biphenyl/orthophenylphenol -As above -Low volatile (orthophenyl phenol, benzyl phenol)

Dyes for PET and Wool Disperse dyes (DD): High temperature –not suitable Low energy DDs-low sublimation fastness Medium energy dyes –pale shades or dyeing at C High energy dyes- not suitable –but can be used for max. colour yield and fastness is required – applied to C prior to PET/wool blending pH : 4.5 – 5.5.

Wool Dyes: Acid and premetallised dyes – most suitable No staining on PET Build up ~ C Complete exhaustion at boil in 30 min. Dye selection is not critical Wet fastness is important : 1:2 metal complex preferred Dyeing pH: 4.5 –5.5

Mixture dyes: Disperse/wool dye mixture- available since 1985, suitable for 55:45 PET/wool Advantages: *simplified selection, reduced weighing/handling of dyes * good reproducibility (from batch to batch or lab.to bulk scale) * tone and tone dyeings as a result of good compatibility of acid and disperse dyes within each mixture *suitable for computer colour matching Single dye class: e.g. reactive disperse dyes Developed dyes show poor light fastness, not commercially suitable

Minimisation of damage to wool The advantages of high temperature dyeing above C are –Fast deep shades –Shorter leveling time –Better levelling –Less staining of wool Disadvantages –Wool degradation –reduction in strength, elongation, abrasion resistance, yellowing

Therefore, to protect the wool component during high temperature dyeing, –Most common agent HCHO (5% owf) allows dyeing at C for 4 hrs C for 3 hrs C for2 hrs C for 1 hr –pH:

Recommended dyeing times C for min with carrier, no formaldehyde C,90 –120 min with carrier and without formaldahyde C, 60 –90 min, reduced amount of carrier, formaldehyde necessary C, min (not >40 min), carrier optional, formaldehyde necessary High temperature dyeing is recommended for deep shades –yellowing is not so critical

Precautions for formaldehyde use –Shades of some dyes are affected -careful dye selection –HCHO vapours are potentially hazardous -restricted use by health and safety considerations Therefore, agents which will release HCHO during dyeing (in-situ release) are preferred. E.g DMEU -HCHO release above 0 0 C

Dyeing methods: One bath dyeing method with disperse and acid or metal complex dyes Dye selection: –Disperse dye –low energy ->minimum staining of wool –easily removed by after wash –Acid or metal complex –not so critical

General dyeing recipe X% disperse dye Y% acid/metal complex dye Z% carrier 1 –2% dispersing agent 5 -10% glauber’s salt pH :4.5 –5.5 with acetic acid

Dyeing procedure Set bath with auxuliaries Preheat 10 –20 min at C Add disperse and dissolved acid dye Treat for 10 min Raise temperature to boil or C min Dye for 1½-2hrs depending on depth of shade Cool, cold and hot rinse –shading C

One-bath dyeing Improve dye exhaustion Minimise wool staining Wool protecting agent is necessary Recipe: –X% disperse dye –Y% acid / metal complex dye –3-5% HCHO (30%) –1-2% dispersing agent, pH : 5 -6 with HAC’

Pretreat with auxiliary at C Add disperse and acid dyes Treat for 10 min Raise temperature to C/120 0 C in 45 min Dye for 30 –60 min

After treatment Staining of wool with disperse dyes cannot be avoided even if the process is carried out with most siutable dyes under the most favourable conditions Disperse staining on wool –poor fastness –must be removed completely One-bath method –reduction clear is not possible After wash: 1-2 gpl non-ionic detergent, pH 5-6 with HAC’, min at 60 0 C, good rinse With deep shades, repeat the above process

Two bath process Used for deep shades -particularly navy and black Dye polyester component with –X % disperse dye –Y% carrier –1 –2% dispersing agent –pH 5-6 with HAC’ –Maximum temperature : C or boil –Cold rinse

Reduction clearing: –3 gpl hydrose – ml/l ammonia(25%) –0.5-1 gpl non-ionic emulsifying agent –For 30 min at C Good rinse, acidify with HAC’ Dyeing of wool component

Thermosol dyeing Not common Can be used for coloration of PET component only Wool component is dyed seperately ( detail sin page ) Dry heat treatment: – C for 45 –60 secs –Not harmful to wool except slight yellowing –Less wool staining

Correction of faulty dyeings Faulty shades can be levelled or partially stripped with X gpl carrier 2-4% levelling agent for wool 1 –2% emulsifying agent pH 5-6% with HAC’ –Treatment at boil for 1 –2 hrs or C for 1 –1 ½ hrs If only shade on wool is to be corrected, carrier is not necessary