12 Energy and Related Savings from Controlled Low Wet Pick-Up Application of Textile Chemicals and Dyes via Semistable Foams
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GEORGE M. BRYANT Union Carbide Technical Center, South Charleston, WV 25303
Interest in low wet pick-up methods for textile finishing and dyeing has burgeoned since the o i l embargo and resultant shortages in 1973-74. A partial listing of the methods employed includes: vacuum extractors (1), air jet-assisted squeeze rolls (2), kiss rolls (3), transfer belts (4), a blast of high velocity gas (the "machnozzle") (5), sprays (6), and foam coating (7, 8, 9). Primary impetus for most of these developments was the reduced energy required in subsequent processing steps, since evaporation of water is by far the most energy intensive step in textile wet finishing (10, 11) and dyeing (11). Other substantial benefits derive from reducing the wet pick-up in wet finishing and continuous dyeing operations. Improved chemical efficiency in resin finishing has been reported by several sources (4, 12, 13, 14), while the relation of water content to dye migration tendency during the drying step of continuous dyeing has been recognized (15, 16). For a current review of prior art low add-on methods, see Leah (16a). Methods which employ l i q u i d phase t r e a t i n g l i q u o r s (spray, t r a n s f e r r o l l s and b e l t s , e t c . ) share a conmon d i f f i c u l t y stemming from the low volume o f l i q u o r i n r e l a t i o n t o t h e l a r g e s u r f a c e area o f t h e f i b e r s comprising t h e s u b s t r a t e t o be t r e a t e d . T h i s d i f f i c u l t y i s acerbated when aqueous l i q u o r s a r e t o be a p p l i e d t o h y d r o p h i l i c f i b e r s . Foam c o a t i n g methods employ s t a b l e foams which allow t h e t h i c k n e s s o f t h e l i q u i d - a i r mixture t o be cont r o l l e d by a doctor b l a d e o r r o l l . Comparatively low add-ons can be achieved by v i r t u e o f t h e low d e n s i t y o f t h e foam l a y e r , but the s t a b l e nature o f such foam, and i t s inmobile l i q u i d phase, i n h i b i t r a p i d , uniform d i s t r i b u t i o n through t h e s u b s t r a t e . 00OTROIIED LOT WET PICK-UP VIA SEME-STABLE FOAMS The use o f semi-stable foams, which have a s h o r t h a l f - l i f e ( i . e . , time f o r h a l f o f t h e contained l i q u i d t o d r a i n from t h e foam) o f the o r d e r o f a few minutes, has made p o s s i b l e a h i g h speed process f o r u n i f o r m l y impregnating f a b r i c s w i t h c o n t r o l l e d ,
0-8412-0509-4/79/47-107-145$05.00/0 © 1979 American Chemical Society
Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
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ENERGY CONSERVATION IN TEXTILE AND POLYMER PROCESSING
lew wet pick-ups o f foamed dyes, r e s i n s and o t h e r chemical substances (17, 18). The a p p l i c a t i o n o f f a s t - w e t t i n g , semis t a b l e foams cannot be c o n t r o l l e d by c o n v e n t i o n a l c o a t i n g methods, but r e q u i r e s t h e use o f a novel a p p l i c a t o r t o c o n t r o l t h e foamf a b r i c contact time (19). The present paper d e s c r i b e s r e s u l t s o b t a i n e d by c o n t r o l l e d , low wet pick-up a p p l i c a t i o n s o f DMDHEU r e s i n formulations and d i s p e r s e dyes t o f a b r i c employing semis t a b l e foam f i n i s h i n g technology (the FET' P r o c e s s ) .
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Features o f t h e FFT A p p l i c a t i o n Process. The h i g h speed FFT Process can be c h a r a c t e r i z e d by c o n s i d e r a t i o n o f t h e key f e a t u r e s o f t h e f e e d l i q u o r , foam and a p p l i c a t o r system employed i n t h e process. Feed L i q u o r C h a r a c t e r i s t i c s : •High c o n c e n t r a t i o n o f f u n c t i o n a l chemicals ( r e s i n , dyes, s o f t e n e r , e t c . ) • Rapid w e t t i n g o f t h e s u b s t r a t e t o be t r e a t e d • Formulated w i t h foaming agents which product f a s t b r e a k i n g semi-stable foam Semi-Stable Foam C h a r a c t e r i s t i c s : • H a l f - l i f e between about 1 and 60 minutes • D e n s i t y i n t h e range 0.3-0.01 g/cc • Bubble diameters i n t h e range 0.05-0.5 nm A p p l i c a t o r System C h a r a c t e r i s t i c s : • Metered r a t e o f d e l i v e r y o f l i q u o r and a i r t o t h e foamer, and o f foam i n t o t h e f a b r i c s u b s t r a t e t o be t r e a t e d • A p p l i c a t o r nozzle design t o p r e c i s e l y c o n t r o l the foam-fabric contact time • Nozzle design t o d e l i v e r foam t o f a b r i c a t a con t r o l l e d r a t e and i n a uniform s t a t e o f r e l a x a t i o n a c r o s s t h e width o f t h e n o z z l e o r i f i c e The foam-fabric contact time, o r t h e machine contact time (ΜΖΓΓ), i s determined by t h e r a t i o o f t h e n o z z l e o r i f i c e dimension i n t h e d i r e c t i o n o f f a b r i c t r a v e l t o the f a b r i c v e l o c i t y : l/rjr =
N
o
z
z
l
e
l e n g t h (cm) F a b r i c Speed (cm/sec)
For t y p i c a l n o z z l e gap dimensions (/~1 cm) and s u b s t r a t e speeds (^•102 can/sec), MCT v a l u e s a r e i n t h e range 1 0 ~ t o 10~3 seconds. 2
C o n d i t i o n s f o r U h i f o i m Substrate Coverage. Foam d e l i v e r e d i n t h e FFT Process t o a f a b r i c s u b s t r a t e a t a given add-on r a t e (per cent by weight) r e q u i r e s a c e r t a i n time t o break and absorb i n t o t h e f a b r i c . The r a t e o f a d s o r p t i o n w i l l depend on t h e foam composition and p r o p e r t i e s , and on t h e composition, s t r u c t u r e and sorbancy o f t h e f a b r i c s u b s t r a t e under t h e c o n d i t i o n s o f a p p l i c a t i o n . F o r a given foam and f a b r i c combination, t h e time
Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
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r e q u i r e d f o r a g i v e n add-on o f foam t o be absorbed i s denoted a s the E q u i l i b r i u m Contact Time (ECT). As the r a t e o f d e l i v e r y o f foam t o the f a b r i c i s i n c r e a s e d , ECT w i l l , o f course, i n c r e a s e . F i g u r e 1 shows an o p e r a t i o n a l method f o r d e f i n i n g ECT f o r a p a r t i c u l a r foam-fabric combination. The necessary c o n d i t i o n f o r uniform coverage o f the t r e a t e d s u b s t r a t e i s :
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ECT^MCT A steady p o s i t i v e pressure i s maintained i n the a p p l i c a t o r n o z z l e when ECT> MCT. F o r c o n d i t i o n s where ECT
