U.S. patent application number 09/963854 was filed with the patent office on 2003-03-27 for trench process and apparatus for dye removal from denim scrap.
Invention is credited to Hall, David M., Hirsch, Gary F., Patton, Robert T..
Application Number | 20030056298 09/963854 |
Document ID | / |
Family ID | 25507814 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030056298 |
Kind Code |
A1 |
Hirsch, Gary F. ; et
al. |
March 27, 2003 |
TRENCH PROCESS AND APPARATUS FOR DYE REMOVAL FROM DENIM SCRAP
Abstract
A trench apparatus and process for liquid treatment of fabric
uses a longitudinal trench for holding a treatment liquid. A pull
rope, chain, or cable having shackle rings or shackles attached
thereto for securing one or more bags to the rope, chain, or cable
is positioned for pulling one or more bags containing dyed fabric
in a longitudinal direction down the length of the trench. The
trench has a liquid treatment zone with a surface level, and the
trench includes one or more raised platforms dividing the trench
into a plurality of separated treatment vats, the raised platforms
having a height extending above said surface level. A conduit
communicates from at least one vat to at least one other vat at a
level below said surface level for movement of liquid therebetween.
A conduit and a pump permits the countercurrent recirculation of
treatment liquor within each longitudinal treatment vat. The bags
can contain dyed scrap such as denim, and the treatment liquid can
be an indigo dye solvent, aqueous reducing solution or aqueous
bleach which is optimally a water-soluble quaternary amine
catalyst, for example.
Inventors: |
Hirsch, Gary F.; (Woodside,
CA) ; Patton, Robert T.; (Lake Jackson, TX) ;
Hall, David M.; (Auburn, AL) |
Correspondence
Address: |
Phillip L Free Jr.
Crowe & Dunlevy
1800 Mid-America Tower
20 North Broadway
Oklahoma City
OK
73102-8273
US
|
Family ID: |
25507814 |
Appl. No.: |
09/963854 |
Filed: |
September 26, 2001 |
Current U.S.
Class: |
8/150 ; 68/10;
68/11; 68/135; 68/157; 68/158; 68/5D; 68/9; 8/147 |
Current CPC
Class: |
D06B 3/00 20130101 |
Class at
Publication: |
8/150 ; 8/147;
68/9; 68/10; 68/5.00D; 68/11; 68/135; 68/158; 68/157 |
International
Class: |
D06B 003/10 |
Claims
The invention claimed is:
1. A trench apparatus for liquid treatment of fabric comprising a)
a longitudinal trench for holding a treatment liquid; b) a pull
rope, chain, or cable having a plurality of shackle rings or
shackles attached thereto for securing one or more bags to the
rope, chain, or cable, the pull rope, chain, or cable being
positioned for pulling one or more bags containing dyed fabric in a
longitudinal direction down the length of the trench, the pull
rope, chain, or cable engaging a pulley, sheave, or sprocket; c) an
untreated fabric platform adjacent one end of the trench and a
treated fabric platform adjacent the other end of the trench.
2. A trench apparatus of claim 1 wherein the trench has a liquid
treatment zone with a surface level, and the trench includes one or
more raised platforms dividing the trench into a plurality of
separated treatment vats, the raised platforms having a height
extending above said surface level;
3. A trench apparatus of claim 2 wherein a conduit communicates
from at least one vat to at least one other vat at a level below
said surface level for movement of liquid therebetween.
4. A trench apparatus of claim 2 wherein liquor recirculation
within an individual vat is accomplished by means of a pump which
takes suction from the upstream end of the individual vat and
discharges into the downstream end of the individual vat.
5. A trench apparatus of claim 2 wherein the raised platforms
within the trench permit adequate residence time of the elevated
fabric containing bas to facilitate optimal draining of the liquor
from the bag.
6. A combination of a trench apparatus of claim 1 and one or more
of said bags containing fabric, wherein the trench has a liquid
treatment zone, the bags being dimensioned when full to block
liquid flow down the trench.
7. A combination of a trench apparatus of claim 1 and one or more
of said bags containing fabric, wherein the fabric is denim
scrap.
8. An apparatus of claim 1 wherein the treatment liquid is a member
selected from the group consisting of dye solvent, aqueous reducing
solution and aqueous bleach.
9. An apparatus of claim 6 wherein the dyed fabric is denim and the
treatment solution is a solvent for water-insoluble indigo.
10. An apparatus of claim 6 wherein the dyed fabric is denim and
the treatment solution is an aqueous solution containing a reducing
agent for indigo.
11. An apparatus of claim 6 wherein the dyed fabric is denim and
the treatment solution is an aqueous bleach for reducing color of
indigo.
12. An apparatus of claim 11 wherein the aqueous bleach is hydrogen
peroxide.
13. An apparatus of claim 11 wherein the aqueous bleach is an
alkali metal hypochlorite.
14. An apparatus of claim 11 wherein the aqueous bleach is a
hydrogen peroxide bleach containing a bleaching catalyst.
15. An apparatus of claim 14 wherein the bleaching catalyst is
water-soluble quaternary amine catalyst.
16. A process for treating fabric with a liquid comprising the
steps of a) moving a bag containing said fabric down a first
longitudinal vat containing liquid at a level wherein longitudinal
movement of liquid in the vat is blocked by the bag, whereby
longitudinal movement of the bag causes liquid to flow through the
bag in a direction counter to the movement of the bag; b) moving
the bag from the vat across a drainage platform to allow excess
liquid to flow from the bag; and c) moving said bag containing said
fabric down a second longitudinal vat containing liquid at a level
wherein longitudinal movement of the bag causes liquid to flow
through the bag in a direction counter to the movement of the
bag.
17. A process for treating fabric with liquid according to claim 16
wherein the dyed fabric is denim, and the liquid is a treatment
liquid which is a member selected from the group consisting of dye
solvent, aqueous reducing solution and aqueous bleach.
18. A process of claim 17 wherein treatment liquid is passed from
the second vat to the first vat in countercurrent movement to the
movement of the bag.
19. A process of claim 16 wherein a plurality of bags are moved
down the first and second vats in sequence.
20. A process of claim 16 for removing dye from fabric carrying
said dye comprising the steps of a) moving a bag containing said
fabric down a first longitudinal vat containing a liquid solvent
for said dye at a level wherein longitudinal movement of liquid in
the vat is blocked by the bag, whereby longitudinal movement of the
bag causes liquid solvent to flow through the bag in a direction
counter to the movement of the bag; b) moving the bag from the vat
across a drainage platform to allow excess liquid solvent to flow
from the bag; c) moving said bag containing said fabric down a
second longitudinal vat containing liquid solvent for the dye at a
level wherein longitudinal movement of the bag causes liquid
solvent to flow through the bag in a direction counter to the
movement of the bag.
21. A process of claim 16 for removing dye from fabric carrying
said dye, wherein the dyed fabric is denim, and the liquid is a
solvent for indigo.
22. A process of claim 16 wherein solvent for the dye is passed
from the second vat to the first vat in countercurrent movement to
the movement of the bag.
23. A process of claim 16 wherein a plurality of bags are moved
down the first and second vats in sequence.
24. A process of claim 16 for removing dye from fabric carrying
said dye comprising the steps of a) moving a bag containing said
fabric down a first longitudinal vat containing an aqueous solution
containing a reducing and solubilizing agent for said dye at a
level wherein longitudinal movement of liquid in the vat is blocked
by the bag, whereby longitudinal movement of the bag causes said
aqueous solution to flow through the bag in a direction counter to
the movement of the bag; b) moving the bag from the vat across a
drainage platform to allow excess aqueous solution to flow from the
bag; and c) moving said bag containing said fabric down subsequent
longitudinal vats containing aqueous solution for the dye at a
level or levels wherein longitudinal movement of the bag causes
said aqueous solution to flow through the bag in a direction
counter to the movement of the bag.
25. A process of claim 20 wherein a pump is used to recirculate
process liquor through a portion of the trench and through any bags
of fabric contained within said portion of trench.
26. A process of claim 20 for removing dye from fabric carrying
said dye wherein the dyed fabric is denim, and the aqueous solution
contains a reducing and solubilizing agent for indigo.
27. A process of claim 20 wherein aqueous solution containing a
reducing and solubilizing agent for said dye is passed from the
second vat to the first vat in countercurrent movement to the
movement of the bag.
28. A process of claim 20 wherein a plurality of bags are moved
down the first and second vats in sequence.
29. A process of claim 20 wherein the trench utilized for the
reduction and extraction of dye is covered with an airtight cover
which retains an inert gas or oxygen depleted gas environment above
the trench and the bags.
30. A process of claim 12 for bleaching fabric carrying said dye
comprising the steps of a) moving a bag containing said fabric down
a first longitudinal vat containing an aqueous solution containing
a bleaching agent for said dye at a level wherein longitudinal
movement of liquid in the vat is blocked by the bag, whereby
longitudinal movement of the bag causes said aqueous solution to
flow through the bag in a direction counter to the movement of the
bag; b) moving the bag from the vat across a drainage platform to
allow excess aqueous solution to flow from the bag; and c) moving
said bag containing said fabric down a second longitudinal vat
containing aqueous solution for the dye at a level wherein
longitudinal movement of the bag causes said aqueous solution to
flow through the bag in a direction counter to the movement of the
bag.
31. A process of claim 30 for bleaching fabric carrying said dye
wherein the dyed fabric is denim, and the aqueous solution contains
a bleaching agent for indigo.
32. A process of claim 30 wherein aqueous solution containing a
bleaching agent for said dye is passed from the second vat to the
first vat in countercurrent movement to the movement of the
bag.
33. A process of claim 30 wherein a plurality of bags are moved
down the first and second vats in sequence.
34. A process of claim 30 wherein the bleaching agent is hydrogen
peroxide bleach containing a bleaching catalyst.
35. A process of claim 34 wherein the bleaching catalyst is water
soluble quaternary amine catalyst.
36. The process of claim 16 wherein dyes, chemicals and reagents
that may assist in enabling optimization of the fabrics of this
invention for utilization in subsequent processes or end use
applications can be added.
37. The process of claim 36 wherein the treatments may contain
humectants, antibacterial agents, lubricants, dyes or tints,
optical brighteners, hand modifiers, antistatic agents and the
like.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] This invention relates to an apparatus and process for
removing indigo dye from denim scrap. In particular, the process of
this invention is directed to a method for removing indigo dyes
from scrap textiles such as denim scrap where the vat dyes have
been applied in a reduced, soluble "leuco" form and oxidized to
precipitate the dye in and on the fabric in an insoluble, or
oxidized, form.
[0003] 2. Background of Related Art
[0004] Cotton and other cellulose scraps produced when cutting
cotton fabrics in clothing manufacture are a waste product
typically buried in landfills or consumed in incinerators.
Gametting to separate and recover the cotton fiber shortens the
fiber length and the products had few uses. As a consequence, over
200 million pounds of denim scrap in the U.S.A. alone, is destroyed
as waste each year.
[0005] U.S. Pat. Nos. 5,376,143 and 5,471,720 describe a process
for recycling denim waste by separating the fibers, preparing a
colored yarn of a blend of the recycled fibers and virgin fibers,
and preparing denim or similarly dyed fabric from the yarn. This
process has not been commercially implemented, perhaps because of
costs of fiber separation and the limitations of the shortened
fibers in the making a strong, durable fabric.
[0006] Many applications of cotton, however, do not require long
fibers. Cotton batting is a popular absorbent because of its
softness and cushioning characteristics and high water absorbency.
It is a preferred component for many industrial, household and
particular medical products such as quilts, upholstery, sanitary
napkins, diapers and medical products such as swabs, bandages and
the like. However, most of these applications require the cotton
fibers be colorless and strong, and a process for recycling cotton
scrap to produce cotton fibers for these applications has not been
commercially feasible because of the difficulties in processing the
scrap. One principal area of difficulty is removal and/or
decolorizing the vat dyes present in many cotton scraps such as
denim.
[0007] Vat dyes consist of colored compounds that are usefully
precipitated on and within cellulosic fibers. These compounds are
reversibly changed to a water-soluble "leuco" state by chemically
reducing them. This is done easily by mixing the dye into a water
solution containing a water-soluble reducing agent such as sodium
hydrosulfite along with alkali such as caustic soda. In a dying
process, the cellulose fiber is typically immersed in such a
reduced, leuco solution, and the dye is allowed to penetrate the
substrate. After this immersion, the fiber is exposed to an
oxidizing environment. Such an environment is air and in one such
process, the yarn, wetted in a leuco solution is draped in long
beams over rolls and exposed to air until the dye and accompanying
reducing agents are oxidized. Dilute hydrogen peroxide is also used
for this oxidation. In each case, the oxidized medium converts the
leuco dye to a water-insoluble state. If the dye molecule is
contained within the cellulose substrate, the water-insoluble dye
is trapped and cannot be removed by casual exposure to water and
detergents.
[0008] Fabric is often dyed with more than one form of leuco dye.
It is a common practice to dye dark shades of indigo first with the
leuco form of black sulfur dye and second with the leuco form of
blue indigo dye. Both dyes require subsequent oxidation to render
them water-insoluble.
[0009] U.S. Pat. No. 5,366,510 describes a process for desizing and
color fading indigo dyed garments by contacting them with a
reducing agent in an aqueous solution to extract dye materials
before the fabrics are bleached to produce the faded, "stone
washed" or "acid washed" appearance popular with denim materials.
The dye is removed in a conventional rotary drum washer-extractor.
Treatment of denim scrap by this procedure tends to produce tightly
rolled up scrap pieces from which all of the dye is not extracted
or to unravel the scraps, producing useless balls and tangles of
yarn and fabric scraps or individual yarn pieces which foul the
washer extractor.
[0010] For the economical recovery of useful products from textile
scraps such as denim scraps, dye removal and recovery is highly
desirable. The value of the recovered dye partially offsets the
costs of the recycling. Also, the recovery removes an undesirable
component from the waste water.
[0011] Solvent removal of dyes from synthetic fabrics is a known
procedure. U.S. Pat. No. 1,839,819 describes a method for removing
dyes from synthetic textiles using heated organic solvents selected
to swell the cellulose acetate and cellulose ether fibers and
remove solvent soluble dyes without any chemical change of the
dyes, thus preserving them for reuse.
[0012] However, an effective solvent extraction system for textile
scraps like denim scraps has not been feasible. The solvent removes
size, softeners, surfactants, finishes and fully oxidized dye from
the fabric, producing a solution of these components. Solvent
evaporation yields a cake or solution of these components which is
useless without a further, expensive purification process.
[0013] In U.S. Pat. No. 5,989,296 a process is described for
removing indigo dye from denim scrap by extracting the fabric with
an organic solvent in which the indigo dye is soluble at elevated
temperatures. In this process, the solvent is cooled and extracted
with an aqueous phase containing a reducing agent, and the aqueous
phase is treated to oxidize and recover the indigo dye or,
alternatively, the dye is recovered from the solvent by
concentration and precipitation.
[0014] U.S. Pat. No. 5,366,510 describes a process for desizing and
color fading indigo dyed garments by contacting them with a
reducing agent in an aqueous solution to extract dye materials
before the fabrics are bleached to produce the faded, "stone
washed" or "acid washed" appearance popular with denim materials.
The dye is removed in a conventional rotary drum washer-extractor.
Treatment of small denim scrap in this procedure tends to unravel
the scraps, producing useless balls and tangles of yarn and fabric
scraps which foul the washer extractor.
SUMMARY
[0015] One object of this invention is a highly effective process
for treating denim scrap with extraction solvents for extracting
the majority of dye from denim to yield a scrap lightly tinted with
indigo dye residue.
[0016] A further object of this invention is a highly effective
process for treating denim scrap with a reducing solution to remove
dye from the fabric.
[0017] Another object of this invention is a highly effective
process for treating denim scrap with a catalyzed hydrogen peroxide
bleaching process to remove the remaining color in the fabric.
[0018] Another object of this invention is the use of a novel,
inexpensive trench apparatus for use in the above processes.
[0019] Another object of this invention is a process for the
countercurrent extraction of dye from fabric scrap, the purpose of
which is to produce extraction liquor effluent containing the
highest possible concentration of dye to facilitate the easiest
subsequent dye recovery step utilizing the most compact and least
expensive equipment.
[0020] Another object of this invention is a process consisting of
a plurality of separated treatment vats, each equipped with a
recirculation pump capable of moving the optimum flow of extraction
liquor through the bags in the vat/trench. This is necessary since
the desired ratio of overall liquor production to overall fabric
treatment rate would not otherwise produce the desired face
velocity of liquor through the fabric bed, i.e. gallons per minute
of liquor per square foot of trench cross sectional area. This
recirculation is accomplished by means of a pump or pumps taking
suction at the bottom of the upstream end of an individual
treatment vat and discharging the liquor at the bottom of the
downstream end of said individual treatment vat.
[0021] A still further object of this invention is a process which
raises the individual bags of liquor saturated fabric above the
level of the liquor in the trench and allows the liquor to drain
from the bag in a direction perpendicular to the normal flow of
liquor in the bag. This has the desirable effect of causing flow of
liquor perpendicular to the mean orientation of parallel pieces of
scrap fabric.
[0022] In summary, the trench apparatus for liquid treatment of
fabric of this invention comprises a longitudinal trench for
holding a treatment liquid. A pull rope, chain, or cable having a
plurality of shackle rings or shackles attached thereto for
securing one or more bags to the rope, chain, or cable is
positioned for pulling one or more bags containing dyed fabric in a
longitudinal direction down the length of the trench. The pull
rope, chain, or cable engages a pulley, sheave, or sprocket. An
untreated fabric platform is adjacent one end of the trench, and a
treated fabric platform is adjacent the other end of the trench.
The trench has a liquid treatment zone with a surface level, and
the trench includes one or more raised platforms dividing the
trench into a plurality of separated treatment vats, the raised
platforms having a height extending above said surface level. A
conduit communicates from at least one vat to at least one other
vat at a level below said surface level for movement of liquid
therebetween. Furthermore, the separation of the trench into
separate vats by means of the raised platforms allows the
recirculation of the liquor contained within each individual vat at
a rate which facilitates the optimum extraction rate of dye from
the scrap fabric. Additionally, the raised platforms cause the
gentle movement of fabric pieces as the bags are pulled over said
platforms. This facilitates the optimum exposure of all surfaces of
individual scrap pieces so as to eliminate the possibility of any
such surface going through the entire extraction process without
seeing an adequate quantity of extraction liquor. Furthermore, the
process of raising each liquor saturated bag above the liquid level
of the liquor in the trench facilitates draining of that liquor
contained within the bag in a direction perpendicular to the normal
flow of liquor through the bag. This process insures an additional
degree of extraction uniformity by providing still more opportunity
for the liquor to flow through the pieces of fabric. The entire
portion of the trench devoted to the extraction of dye by means of
a reducing agent may be advantageously covered with an airtight
cover which retains an inert gas or an oxygen depleted atmosphere.
This has the effect of eliminating the useless reaction of oxygen
with either the leuco form of the dye or with the reducing agent
itself.
[0023] The trench apparatus can be used to treat one or more of
said bags containing fabric, and the trench has a liquid treatment
zone, the bags being dimensioned when full to block liquid flow
down the trench.
[0024] In a preferred embodiment, one or more of said bags contain
denim scrap. The denim scraps within the bags will lie essentially
parallel to each other in such a manner that the scrap pieces are
prevented from coiling, balling or becoming distorted during the
treatments.
[0025] The treatment liquid can be a dye solvent, aqueous reducing
solution of aqueous bleach, or dyes, chemicals or reagents that may
assist in enabling optimization of the fabrics of this invention
for utilization in subsequent processes or end use applications,
for example. In a preferred embodiment, the dyed fabric is denim,
and the treatment solution is a solvent for water-insoluble indigo.
In another preferred embodiment, the dyed fabric is denim, and the
treatment solution is an aqueous solution containing a reducing
agent for indigo.
[0026] In a still further embodiment, the dyed fabric is denim, and
the treatment solution is an aqueous bleach for reducing color of
indigo. The aqueous bleach can be a hydrogen peroxide bleach which
may contain a bleaching catalyst which is optimally a water-soluble
quaternary amine catalyst.
[0027] In summary, the process of this invention for treating
fabric with a liquid comprises the steps of (a) moving a bag
containing said fabric down a first longitudinal vat containing
liquid at a level wherein longitudinal movement of liquid in the
vat is blocked by the bag, whereby longitudinal movement of the bag
causes liquid to flow through the bag in a direction counter to the
movement of the bag; (b) moving the bag from the vat across a
drainage platform to allow excess liquid to flow from the bag; (c)
moving said bag containing said fabric down a second longitudinal
vat containing liquid at a level wherein longitudinal movement of
the bag causes liquid to flow through the bag in a direction
counter to the movement of the bag; and (d) recirculating the
liquid within each vat by means of a pump in a direction opposite
to the movement of the fabric bags. In one embodiment, the dyed
fabric is denim, and the liquid is a treatment liquid which is a
member selected from the group consisting of dye solvent, aqueous
reducing solution or aqueous bleach or dyes, chemicals or reagents
that may assist in enabling optimization of the fabrics of this
invention for utilization in subsequent processes or end use
applications.
[0028] In summary, the process of this invention for removing dye
from fabric carrying said dye comprises the steps of (a) moving a
bag containing said fabric down a first longitudinal vat containing
a liquid solvent for said dye at a level wherein longitudinal
movement of liquid in the vat is blocked by the bag, whereby
longitudinal movement of the bag and recirculation by means of a
pump causes liquid solvent to flow through the bag in a direction
counter to the movement of the bag; (b) moving the bag from the vat
across a drainage platform to allow excess liquid solvent to flow
from the bag; and (c) moving said bag containing said fabric down a
second longitudinal vat containing liquid solvent for the dye at a
level wherein longitudinal movement of the bag causes liquid
solvent to flow through the bag in a direction counter to the
movement of the bag. In one embodiment, the dyed fabric is denim,
and the liquid is a solvent for indigo.
[0029] In another embodiment of the process of this invention for
removing dye from fabric carrying said dye comprises the steps of
(a) moving a bag containing said fabric down a first longitudinal
vat containing an aqueous solution containing a reducing and
solublizing agent or said dye at a level wherein longitudinal
movement of liquid in the vat is blocked by the bag, whereby
longitudinal movement of the bag causes said aqueous solution to
flow through the bag in a direction counter to the movement of the
bag; (b) moving the bag from the vat across a drainage platform to
allow excess aqueous solution to flow from the bag; and (c) moving
said bag containing said fabric down a second longitudinal vat
containing aqueous solution for the dye at a level wherein
longitudinal movement of the bag and recirculation of the solution
by means of a pump causes said aqueous solution to flow through the
bag in a direction counter to the movement of the bag. In one
embodiment, the dyed fabric is denim, and the aqueous solution
contains a reducing and solublizing agent for indigo.
[0030] In another embodiment, the process of this invention for
bleaching fabric carrying said dye comprises the steps of (a)
moving a bag containing said fabric down a first longitudinal vat
containing an aqueous solution containing a bleaching agent for
said dye at a level wherein longitudinal movement of liquid in the
vat is blocked by the bag, whereby longitudinal movement of the bag
and recirculation of the solution by means of a pump causes said
aqueous solution to flow through the bag in a direction counter to
the movement of the bag; (b) moving the bag from the vat across a
drainage platform to allow excess aqueous solution to flow from the
bag; and (c) moving said bag containing said fabric down a second
longitudinal vat containing aqueous solution for the dye at a level
wherein longitudinal movement of the bag and recirculation of the
solution by means of a pump causes said aqueous solution to flow
through the bag in a direction counter to the movement of the bag.
In one embodiment, the dyed fabric is denim, and the aqueous
solution contains a bleaching agent for indigo. The bleaching agent
can be hydrogen peroxide bleach containing a bleaching catalyst,
optimally water-soluble quaternary amine catalyst.
[0031] In another embodiment, the fabric is bleached and/or
decolorized (or partially decolorized) denim fabric and the trough
solution contains dyes, chemical or reagents that may assist in
enabling optimization of the fabrics of this invention for
utilization in subsequent processes or end use applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic longitudinal cross-sectional view of
an abbreviated trench processing system according to an aspect of
this invention.
[0033] FIG. 2 is a top view of the trench processing system of FIG.
1 according to an aspect of this invention.
[0034] FIG. 3 is a cross-sectional view of a section of the trench
processing system of FIG. 1 according to an aspect of this
invention.
[0035] FIG. 4 is a cross-sectional view of the trench taken along
the line 4-4 in FIG. 3 according to an aspect of this
invention.
[0036] FIG. 5 is a cross-sectional view of the trench and fabric
treatment bag taken along the line 5-5 in FIG. 3 according to an
aspect of this invention.
[0037] FIG. 6 is a view of a typical scrap bag 16 according to an
aspect of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0038] The process of this invention is described hereinafter in
terms of extracting dye from denim scrap and bleaching denim scrap
because it is more demanding and requires description of more
details than extracting and bleaching of dyed unfinished and
finished cellulose fiber products such as clothing. Dye removal and
bleaching of denim garments is desired to product products having a
faded "stone-washed" appearance, for example. It will be readily
understood to a person skilled in the art that the process of this
invention can be applied to remove all or only a portion of the
color in a dyed fabric or garment of cellulose or other material
and all of these bleaching applications are intended to be included
within the scope of this invention.
[0039] FIG. 1 is a schematic longitudinal cross-sectional view of
an abbreviated trench processing system of this invention, and FIG.
2 is a top view thereof. The trench system is a series of
longitudinal elongated vats 2 optionally separated by raised drain
platforms 4 with an untreated bag support platform 6 at the staging
end and a processed bag support region of platform 8 at the
receiving end. A drum pulley 12 driven by motor mounted on platform
8 reels in the endless loop of draw rope or cable 14. The draw rope
14 has rings 15 attached to it for shackling to bags filled with
scrap 16 as shown in greater detail in FIG. 6. A matching drum
pulley 18 supported on platform 6 reels and/or returns the draw
rope to the staging platform for attachment of bags of scrap
awaiting processing. The bags 16 are drawn through treatment liquid
10 in each vat.
[0040] Each vat has a liquid inlet pipe 17 and an outlet pipe 19,
the outlet pipe from one vat being connected with a valve 21 to the
inlet pipe of the adjacent vat for movement of liquid in a
direction through the series of vats in a direction counter to the
direction of movement of the bags 16. Additionally, each vat has a
recirculation line 23 with a pump 25 which is used to recirculate
liquor from the bag inlet end of the vat to the bag outlet end. The
vats can have bottoms at the same elevation or they can
progressively lower elevations in the direction of the liquid flow
to use gravity to move the liquid between vats. Similarly, the
bottom of each vat can be level or be sloped slightly upward in the
direction of bag movement to facilitate liquid flow in the counter
current direction. FIG. 3 is a cross-sectional view of a section of
the trench processing system of FIG. 1.
[0041] Each treatment vat 2 has a sloped inlet end 20 down which
each bag is drawn into the treatment liquid, a flat bottom 21, and
a sloped outlet end 22 up which each bag is drawn to a draining
platform 8.
[0042] FIG. 4 is a cross-sectional view of the trench taken along
the line 4-4 in FIG. 3, and FIG. 5 is a cross-sectional view of the
trench and fabric treatment bag taken along the line 5-5 in FIG. 3.
The bottom of the vat has a curved shape to which the bags conform.
The treatment liquid level 26 is lower than the top 28 of the bag
so the bag acts as a plug, forcing the liquid to flow through the
contents of each bag as the bag is drawn through the vat.
[0043] FIG. 6 is a view of a typical bag 16. The bags have a
conventional open mesh construction sufficiently close to retain
the fabric scraps but not so close as to impede liquid flow. Each
bag has a loop 34 which is attached by shackle 35 to ring 15 fixed
to draw rope 14. Scrap typically has irregular shapes and sizes,
and for uniform processing, cutting the fabric pieces, although not
necessary, may be desirable. The scraps can be cut or chopped into
these pieces using conventional fabric chopping equipment.
[0044] Because of the size and construction of the pieces of denim
scrap, it is difficult to accomplish uniform processing in the bath
processes for dye removal and bleaching. Denim is a twill fabric,
hence is not a symmetrical weave. On the face side of the fabric,
more warp yarn is exposed than fill yarn and on the other side,
more fill yarn is exposed than warp yarn. In indigo dyed denim, the
warp yarn is heavily dyed, and the fill yarn is undyed. Because of
the asymmetry in construction and the different chemical history of
the yarns, when denim scraps are wetted with solvent and agitated
in a free state, they tend to curl and roll into spirals of fabric,
sometimes tightly. A tightly wound spiral allows poor access in a
circulating agitation bath since inner portions are shielded by the
outer layers. As a further problem, agitation tends to unravel the
scraps, producing useless balls and tangles of yarn, yarn pieces
and fibers which foul the bath components.
[0045] This problem is solved by use of a trench treatment
apparatus in the process of this invention because the liquid
contact with the fabric and removal or bleaching of the dye
molecules occurs in the slow moving liquid by a combination of
liquid flow and diffusion which is not significantly impeded by the
conformation of the fabric. Prolonged contact of the liquid with
the fabric achieves the result. Furthermore, the fabric is not
frayed by the slow movement of the liquid through the bag.
Additionally, the packing configuration of the fabric pieces within
the bag prevents fabric movement and no curling problems occur.
[0046] Referring to FIGS. 1 and 2, after the denim scrap is placed
in the mesh bag 16, the bag is placed on the untreated fabric
platform 6 and shackled to the draw rope 14. The draw rope 14 pulls
the filled bag slowly into the first vat 2 where it is thoroughly
wetted by the treatment liquid 10. The bag plugs the vat and
extends above the top surface of the liquid 10. As the slow bag
movement continues, the bag is very slowly drawn through the vat,
liquid is pushed down the vat by the bag, raising the liquid level
in front of the bag, the difference in liquid level causing the
liquid to flow by gravity through the contents of the bag.
Additionally, liquid is removed from the inlet end of the vat,
passes through conduit 23, and is discharged into the outlet end of
the vat by means of a pump 25. This increases the flow of liquid
through the bag to a flow rate in excess of that produced by bag
movement alone. As the bag movement continues, the bag is drawn up
onto platform 8, above the liquid level, and the excess liquid
drains from the bag. The bag is then drawn into the next vat of the
series where the process is repeated until the bag is drawn from
the final vat onto the treated fabric platform 8. The treatment
liquid flows through the series of vats in a direction counter to
the direction of movement of the fabric-filed bags, fresh liquid
being introduced at the end of the last vat adjacent the treated
fabric platform 8 to effect final treatment of the fabric with
fresh liquid. The liquid is passed from vat to vat through the
conduits 19 and 17 until its removal from the vat system adjacent
the untreated fabric platform 6. In this manner, for dye removal by
an aqueous reducing solution, the liquid removed from the system
has the maximum concentration of dye, facilitating dye recovery,
and the fabric from which the dye has been mostly removed has a
final exposure to clean reducing solution. Similarly, for
bleaching, the fabric at the end of the process is exposed to a
maximum strength bleaching solution while the fabric first being
introduced to the system has the maximum amount of dye and is
exposed to a bleaching solution which can be almost exhausted. This
is desirable to effect maximum bleaching efficiency with the
chemical bleaching reagent.
[0047] It will be readily apparent to a person skilled in the art
that any number of vats can be used, and special pretreatment vats
and final, rinsing vats can be interposed with separate liquid
supplies and waste lines, if the process requires these additional
steps. The vats can be provided with conventional heating coils to
maintain the vat solutions at a pre-selected elevated temperature,
if desired.
[0048] Aqueous Dye Extraction Using a Reducing Agent
[0049] This process applies certain portions of the process of U.S.
Pat. No. 5,366,510, the entire contents of which are hereby
incorporated by reference. After the denim scrap is placed in a bag
16 and the bag are shackled to a ring 15, the bag is pulled into
the adjacent vat into contact with an aqueous reducing solution. As
the bag is pulled through a succession of vats and drain platforms
and a stream of reducing agent solution slowly flows through the
bag, the water-insoluble dye in the fabric is reduced by the
reducing agent in the solution to a water-soluble form which then
dissolves in the aqueous solvent and is removed from the fabric by
diffusion and/or liquid movement.
[0050] The extraction solution is an aqueous solution of a reducing
agent, preferably at an elevated temperature of about 80.degree. C.
to 95.degree. C. Depending upon the subsequent dye recovery
process, advantageously a dye complexing agent such as polyvinyl
pyrrolidone may be added to prevent redeposit of the degraded
dye.
[0051] Suitable reducing agents which are useful for desizing
starch type sizing and removing indigo and other vat dyes from
denim scraps include alkali metal hydrosulfites, for example,
sodium hydrosulfite; alkali metal sulfoxylate formaldehyde such as
the sodium salt, thiourea dioxide, and the like.
[0052] Reducing agents which are primarily useful for removing the
indigo and other vat dyes include alkali metal hydrogen sulfites,
sulfides, thiosulfates, oxalates, hydrosulfites and
hydrosulfides.
[0053] The most useful compounds for vat dyes are sodium
hydrosulfite and sodium sulfoxylate formaldehyde and, for sulfur
dyes, sodium sulfide.
[0054] Advantageously, sodium or zinc sulfoxylate formaldehyde is
applied under either acid or basic conditions, and sodium
hydrosulfite is used under basic conditions.
[0055] The amount of the reducing agent to be used is not critical,
but stronger solutions are more efficient. A solution of from 0.5
to 20 grams per liter of thiourea dioxide or from 0.5 to 20 grams
per liter of sodium hydrosulfite is suitable.
[0056] The reducing agent converts the indigo and other vat dyes in
the fabric to their water soluble state, and the dye is carried
into solution, removed from the fabric and passed to the drain from
which it is captured for dye recovery.
[0057] Catalyzed Alkaline Hydrogen Peroxide Bleaching
[0058] After removal of the reducing solutions and rinsing with
water to remove any remaining free-floating dye, the bags 16 can be
placed into a second series of vats having the structure shown in
FIGS. 1 and 2 where they are drawn through a catalyzed hydrogen
peroxide bleaching solution. It will be readily apparent to a
person skilled in the art that the rinse treatment and the
catalyzed hydrogen peroxide bleaching solutions can be provided in
an extension of the dye removal vats or in a separate series having
the same or a similar structure, and all configurations of vats and
treatment solutions are intended to be included within the scope of
this invention.
[0059] The hydrogen peroxide bleaching solution should have a
concentration of hydrogen peroxide of from 0.2% to 3.0%. The
concentration range is preferably from 0.25% to 1.0%. The solution
pH is preferably within the range of from 10.5 to 11.2, and the
process water temperature is preferably within the range of from
75.degree. to 95.degree. C. The addition of catalysts demands that
the pH be maintained somewhat lower with catalyst than without
catalyst, for example 10.7 with catalyst and 11.0 without. The use
of higher temperatures accelerates the bleaching regardless of
catalyst and improves the whiteness achieved.
[0060] This invention is based on the discovery that with
appropriate catalysts, hydrogen peroxide can effectively decolorize
dyes which have been selected to be oxidation resistant, even dyes
which are routinely insolubilized with hydrogen peroxide without
loss of color. And even more surprisingly, very satisfactory
decolorizing is obtained without significant loss of fiber strength
or fiber quality.
[0061] Suitable catalysts include transition metal ions, preferably
cupric and stannic ions. Other transition metal ions such as
chromium, cobalt and nickel also exhibit catalyst activity. The
concentration of catalyst must be sufficient to catalyze the
bleaching reaction but should be insufficient to cause spontaneous
and rapid decomposition of the hydrogen peroxide. A catalyst
concentration of from 0.1 to 2 ppm is usually operable and a
concentration of from 0.3 to 0.7 ppm is preferred. Careful control
of catalyst concentration is required.
[0062] Because these metal ion catalysts cause decomposition of the
hydrogen peroxide at higher concentration, quantities of
transitional metal ions normally present in conventional water can
cause serious problems. Removal of these ions by ion exchange is
usually necessary prior to the addition of the desired level of
catalyst.
[0063] Chelates are coordination compounds having a multidentate
ligands, that is, ligands which bond to a metal atom at more than
one place in a process termed chelation. Any water-soluble
chelating agent effective to complex and deactivate the catalytic
activity of transition metal ions can be used. Suitable
water-soluble chelating agents are EDTA (ethylenediaminetetraacetic
acid) and NTA (nitrilotriacetic acid).
[0064] Water-soluble quaternary amines are preferred catalysts
because they are not significantly complexed and deactivated by
conventional chelating agents. Suitable water-soluble quaternary
amines include lower alkyl ammonium halides and their derivatives
such as hydroxy and epoxy substituted (lower alkyl)
trimethylammonium halides such as substituted
propyltrimethylammonium chlorides. Preferred quaternary amines for
use in the process of this invention are
dihydroxypropyltrimethylammoniumchlorid- e,
chlorohydroxypropyltrimethylammoniumchloride and
epoxypropyltrimethylammoniumchloride, for example.
[0065] These quaternary amine catalysts have been used to catalyze
hydrogen peroxide bleaching of wood pulp. Wood pulp cellulose
pigments are not selectively resistant to hydrogen peroxide, and
the unique action of catalyzed hydrogen peroxide on vat dyes would
not be predicted or suggested by their action in wood pulp.
[0066] The concentration of the quaternary amines in the hydrogen
peroxide solution should be from 0.1 to 1.0% and is preferably from
0.1% to 0.5%.
[0067] Following the hydrogen peroxide bleaching, rinse water is
passed through the scrap bed to remove residual bleach and
catalyst. Following the washing step, treatment of the decolorized
denim fabric with dyes, chemicals and reagents that may assist in
enabling optimization of the fabrics of this invention for
utilization in subsequent processes or end use applications can be
added. Thus, the treatments may contain humectants, antibacterial
agents, lubricants, dyes or tints, optical brighteners, hand
modifiers, anti-static agents and the like.
[0068] After completion of the extraction, and if applied, the
bleaching process, the bags are removed from the final solution and
squeezed in a hydraulic press to reduce the rinse water content,
the bag emptied, and the scrap fragments are treated to remove
residual water or solution, that is, dried. The dried fragments are
then passed through a conventional garnetting machine or similar
device to separate the individual bleached cotton fibers.
Subsequent processing will be determined by the desired use of the
fibers. For production of yarn, the fibers are preferably blended
with longer virgin fibers, carded and spun into yam by conventional
procedures. For medical cotton applications, the fibers are
processed by the traditional manufacturing procedure developed for
each use.
[0069] The process of this invention is further shown by the
following specific but non-limiting examples.
EXAMPLE 1
Desizing and Dye Removal
[0070] For this process, a vinyl ester or epoxy FRP lined trench
with a glass smooth gel coat backed by 2 inches of magnesite
insulation and properly reinforced concrete is constructed. The
trench is 4 feet wide and 9 feet deep (inside dimensions). At
either end of the trench is a raised ground level platform 8 feet
long. On the inlet end of the trench, the raised platform is used
for loading incoming bags, and on the outlet end of the trench, the
raised platform is used for removing outgoing bags. Immediately
after the incoming bag platform the bottom of the trench slopes
downward at a 450 angle to a flat bottom 10 feet deep and 6 feet
long. This forms a deep vat which contains only water, not
extraction liquor. Immediately before the outgoing bag platform is
a similar deep section of trench, or vat, which is 8 feet long and
10 feet deep, and contains only water. These two vats which contain
only water are used to effect water seals for the trench cover.
Over the entire top of the trench is an insulated FRP lid with two
inches of magnesite insulation that covers not only the trench, but
also the pull rope and suspension pulleys for the pull rope. At
each end of the trench, the pull rope and also the fabric bags drop
below the level of the water in the vat. At each end of the FRP
lid, the bottom edge extends downward below the surface of the
water in the vat. Because the trench cover is sealed along the
sides, the water seal on either end of the trench completely
isolates the atmosphere inside of the cover and above the trench
from surrounding air which contains oxygen. Because the sodium
hydrosulphite solution within the trench reacts with atmospheric
oxygen, this cover allows the air within to become almost
completely depleted of oxygen content.
[0071] The water-containing vat on the bag discharge end also acts
as a rinse chamber. Water is recirculated at 80 gallons per minute
and 95.degree. C. through the fabric bag in the discharge water
vat, and residual sodium hydrosulphite solution is removed. Water
is fed to this water vat at the rate of 2000 gallons per hour and
leaves as effluent at the same rate. Immediately before this rinse
vat, there are two other rinse vats with 8 ft. flat bottoms and
separated from preceding and following vats by 4 foot long, 4-1/2
foot high flat topped platforms. The fronts and backs of each of
these raised platforms slope seamlessly downward at 45.degree.
angles to the bottoms of the longitudinal vats. The makeup water is
fed to the last vat in the direction of bag movement and removed
from the first vat. The used rinse water contains caustic, sodium
hydrosulfite, and some dye and therefore advantageously is piped
directly to the last dye extraction vat as makeup water for the
extraction liquor.
[0072] The extraction section of the trench consists of four vats,
9 feet deep with 8 feet flat bottoms. These vats are separated by
raised platforms, 4-1/2 feet high with four foot flat tops. The
fronts and backs of each of these raised platforms slope seamlessly
downward at 45.degree. angles to the flat bottoms of the vats. In
this manner, the trench is divided into longitudinal vats through
which bags of fabric are pulled. CPVC or other corrosion resistant
piping is attached to slots at each end of the bottom of each
longitudinal vat in such a manner that liquid may pass from vat to
vat bypassing each raised platform. Additionally, the drain slot at
the bag inlet end of each vat is connected to a corrosion resistant
pump which discharges through piping to a liquor inlet slot at the
bag outlet end. The liquor inlet slot extends across the full width
of the trench, and in operation, liquor is forced upward through
each bag as it passes over the slot. The pump suction slot extends
across the full width of the trench, and in operation, pulls liquid
downward through each bag as it passes over the slot. In this
manner, liquor may be recirculated through each vat in a direction
opposite to the direction of movement of the bags.
[0073] Heavy polyester mesh bags with approximately 1/4 inch
openings are fabricated having dimensions such that pulling a full
bag through the trench forms a cubic fabric plug of approximately 4
ft. height, width, and length. The bags are loaded with
approximately 720 pounds of denim cutting room scrap dyed with both
indigo dye and black sulfur dye. Before loading into the bags, the
cutting room scrap is cut into pieces with an average maximum
dimension of 2 inches.
[0074] Bags are attached by rope loops and shackles to heavy metal
stainless steel rings located down the draw rope at 8 foot
intervals. The bag interval is therefore one bag every 8 feet. The
draw rope is held suspended on pulleys at an elevation slightly
below the top of the trench. The draw rope consists of a continuous
loop which is pulled by a sheave at a rate of 0.37 ft. per
minute.
[0075] Each of the longitudinal vats is recirculated by means of a
pump at a rate of 80 gallons per minute. This gives an average 5
gallons per minute per square ft. face velocity of liquor passing
through the bag. Liquor is passed through the entire extraction
trench at a rate of 2000 gallons per hour. This liquor is pumped
into the vat at the end of the trench from which the bags go into
the rinse section. Discharge liquor containing a high concentration
of dye is pumped out of the vat at 2000 gallons per hour at the end
where the bags are fed into the trench process. This high
concentration of dye in the liquor effluent facilitates easy
subsequent recovery of the dye and a minimal use of water in the
process. The incoming extraction liquor is made up of 2000 gallons
per hour at 95.degree. C. water, 295 pounds of 380 Baume caustic
soda solution, 50 pounds of 95% sodium hydrosulfite, and 23 pounds
of Amwet PTH wetter solution (made by American Emulsions) and 28
pounds of 40% polyvinylpyrrolidone. As the liquor passes into each
subsequent longitudinal vat, 20 pounds of sodium sulfite and 24
pounds of 38.degree. Baume caustic soda are added. This replaces
that sodium sulfite which naturally degrades with time and adjusts
the pH because of the added reagent.
[0076] As the bags of fabric leave the extraction trench, they are
uniformly depleted of indigo and black sulfur dyes, and the fabric
is a very light blue. At this point, it is ready for bleaching with
either a peroxide or a sodium hypochlorite bleach process.
EXAMPLE 2
Catalyzed Hydrogen Peroxide Bleaching
[0077] Bags containing very light blue denim scrap that has been
desized and from which the dye has been extracted are moved from
the extraction and desizing device to the end of a bleaching
trench. For this process, a vinyl ester or epoxy FRP lined trench
with a glass smooth gel coat backed by 2 inches of magnesite
insulation and properly reinforced concrete is constructed. The
trench is 4 feet wide and 9 feet deep (inside dimensions). At
either end of the trench is a raised ground level platform 8 feet
long. On the inlet end of the trench, the raised platform is used
for loading incoming bags, and on the outlet end of the trench, the
raised platform is used for removing outgoing bags. The entire
length of trench is covered with a FRP lid backed with two inches
of urethane foam insulation.
[0078] Immediately before the outgoing bag platform the trench
slopes down to a flat bottomed vat which is 8 feet long, 9 feet
deep, and contains wash water. Water is recirculated at 80 gallons
per minute and 95.degree. C. through the fabric bag in the
discharge water vat, and residual bleach bath liquor is removed.
Water is fed to this water vat at the rate of 2000 gallons per hour
and leaves as effluent at the same rate. Immediately before this
rinse vat, there are two other rinse vats of the same dimensions.
All of the rinse vats are separated by raised platforms 4-1/2 ft.
above the bottom of the trench and 4 feet long. The front and back
of each of these raised platforms slope seamlessly downward at
45.degree. angles. The resulting troughs, or vats, between raised
platforms are 8 feet long. The makeup water is fed to the last vat
in the direction of bag movement and removed from the first vat.
The used rinse water contains caustic, peroxide, sequesterant, and
some bleach bath chemicals and therefore advantageously is piped
directly to the bleach vats as makeup water. To the first rinse
vat, the one nearest the bleach vat, is added 17 pounds per hour of
60% acetic acid, 50 pounds of Delimol NSR (wetting and scouring
agent manufactured by BASF), and 21 pounds of Delimol 9208 (dye
dispersant and water sequesterant manufactured by BASF). Each rinse
vat has its own recirculation pump. The recirculation pump passes
the rinse water through the bags at 80 gallons per minute and
washes bleach bath liquor from the bags. Because each rinse vat has
its own recirculation pump, the bleach bath liquor concentration is
highest in the first rinse vat and lowest in the last rinse vat.
The rinse water, moving counter to the direction of bag movement
passes from the first rinse vat to the last bleach vat. Acetic acid
is added to the makeup water in the rinse bath to neutralize the
alkalinity coming into the rinse vats from the bleach vats.
[0079] Before the rinse vats in the direction opposite to bag
movement, the trench consists of three bleaching vats. The
bleaching vats have flat bottoms which are 8 feet long and are
separated by raised platforms 4-1/2 feet across the top with both a
front surface and a back surface which slope seamlessly downward at
45 degrees to the flat bottoms of the vats. In this manner, the
trench is divided into longitudinal vats through which bags of
fabric are pulled. CPVC or other corrosion resistant piping is
attached to slots at each end of the bottom of each longitudinal
vat in such a manner that liquid may pass from vat to vat bypassing
each raised platform. Additionally, the drain slot at the bag inlet
end of each vat is connected to a corrosion resistant pump which
discharges through piping to a liquor inlet slot at the bag outlet
end. The liquid inlet slot extends across the full width of the
trench, and in operation, liquor is forced upward through each bag
as it passes over the slot. The drain slot extends across the full
width of the trench, and in operation, pulls liquid downward
through each bag as it passes over the slot. In this manner, liquor
may be recirculated through each vat in a direction opposite to the
direction of movement of the bags.
[0080] Heavy polyester mesh bags with approximately 1/4 inch
openings are fabricated having dimensions such that pulling a full
bag through the trench forms a cubic fabric plug of approximately 4
ft. on each side. The bags are loaded with approximately 720 pounds
of denim cutting room scrap originally dyed with both indigo dye
and black sulfur dye, but from which most of the dye has been
extracted utilizing a reducing agent. This cutting room scrap
consists of pieces with an average maximum dimension of 2
inches.
[0081] Bags are attached by rope loops and shackles to heavy metal
stainless steel rings located down the draw rope at 8 foot
intervals. The bag interval is, therefore, one bag every 8 feet.
The draw rope is held suspended on pulleys at an elevation slightly
below the top of the trench. The draw rope consists of a continuous
loop which is pulled by a sheave at a rate of 0.37 ft. per
minute.
[0082] Each of the longitudinal vats is recirculated by means of a
pump at a rate of 80 gallons per minute. This gives an average 5
gallons per minute per square ft. face velocity of liquor passing
through the bag. Makeup liquor is fed to the bleaching vats from
the rinse vats at a rate of 2000 gallons per hour. This liquor is
pumped into the bleach vat immediately upstream (i.e. counter to
bag movement) of the first rinse vat. To the makeup liquor coming
from the rinse section is fed 168 lbs./hr. of 35% hydrogen
peroxide, 134 lbs./hr. of 38.degree. Baume caustic soda, and 84
pounds of 20% dihydroxyporpyltrimethylammonium chloride
solution.
[0083] The bleach bath liquor is level controlled to a pump which
removes it from the first bleach vat. This liquor is then treated
in such a way as to render it acceptable for disposal and is
discharged into the plant waste water stream.
[0084] The fabric scrap has been bleached to a uniform CIE
brightness of 85 and is ready for dewatering and drying.
EXAMPLE 3
Sodium Hypochlorite Bleaching
[0085] Bags containing very light blue denim scrap that has been
desized and from which the dye has been extracted are moved from
the extraction and desizing device to the end of a bleaching
trench. For this process, a vinyl ester or epoxy FRP lined trench
with a glass smooth gel coat backed by 2 inches of magnesite
insulation and properly reinforced concrete is constructed. The
trench is 4 ft. wide and 9 ft. deep (inside dimensions). At either
end of the trench is a raised ground level platform 8 ft. long. On
the inlet end of the trench, the raised platform is used for
loading incoming bags, and on the outlet end of the trench, the
raised platform is used for removing outgoing bags. The entire
length of trench is covered with a FRP lid backed with 2 inches of
urethane foam insulation.
[0086] Immediately before the outgoing bag platform the trench
slopes down to a flat bottomed vat which is 8 feet long, 9 ft.
deep, and contains wash water. Water is recirculated at 80 gallons
per minute and 95.degree. C. through the fabric bag in the
discharge water vat, and residual bleach bath liquor is removed.
Water is fed to this water vat at the rate of 2000 gallons per hour
and leaves as effluent at the same rate. Immediately before this
rinse vat, there are two other rinse vats of the same dimensions.
All of the rinse vats are separated by raised platforms 4-1/2 ft.
above the bottom of the trench. The front and back of each of these
raised platforms slope seamlessly downward at 45.degree. angles to
the flat bottoms of the adjacent vats. The makeup water is fed to
the last vat in the direction of bag movement and removed from the
first vat. The used rinse water is discharged into the plant waste
water effluent stream for proper treatment and disposal. To the
first rinse vat, the one nearest the bleach vat, is added 10 pounds
per hour of 60% acetic acid and 25 pounds of sodium thiosulfate.
Each rinse vat has its own recirculation pump. The recirculation
pump passes the rinse water through the bags at 80 gallons per
minute, washes bleach bath liquor from the bags, and neutralizes
any remaining sodium hypochlorite bleach. Acetic acid is added to
the makeup water in the rinse bath to neutralize the alkalinity
coming into the rinse vats from the bleach vats.
[0087] Before the rinse vats in the direction opposite to bag
movement, the trench consists of three bleaching vats. Each
bleaching vat has a flat bottom 8 feet long, and at both ends slope
upward at 45.degree. angles to form raised platforms 4 ft. in
length across the top and approximately 4-1/2 ft. above the bottom
of the trench. In this manner, the trench is divided into
longitudinal vats through which bags of fabric are pulled. CPVC or
other corrosion resistant piping is attached to slots at each end
of the bottom of each longitudinal vat in such a manner that liquid
may pass from vat to vat bypassing each raised platform.
Additionally, the drain slot at the bag inlet end of each vat is
connected to a corrosion resistant pump that discharges through
piping to a liquor inlet slot at the bag outlet end. The liquor
inlet slot extends across the full width of the trench, and in
operation, liquor is forced upward through each bag as it passes
over the slot. The drain slot extends across the full width of the
trench, and in operation, pulls liquid downward through each bag as
it passes over the slot. In this manner, liquor may be recirculated
through each vat in a direction opposite to the direction of
movement of the bags.
[0088] Heavy polyester mesh bags with approximately 1/4 inch
openings are fabricated having dimensions such that pulling a full
bag through the trench forms a cubic fabric plug of approximately 4
ft. on each side. The bags are loaded with approximately 720 pounds
of denim cutting room scrap originally dyed with both indigo dye
and black sulfur dye, but from which most of the dye has been
extracted utilizing a reducing agent. This cutting room scrap
consists of pieces with an average maximum dimension of 2
inches.
[0089] Bags are attached by rope loops and shackles to heavy metal
stainless steel rings located down the draw rope at 8 foot
intervals. The bag interval is, therefore, one bag every 8 feet.
The draw rope is held suspended on pulleys at an elevation slightly
below the top of the trench. The draw rope consists of a continuous
loop which is pulled by a sheave at a rate of 0.37 ft. per
minute.
[0090] Each of the longitudinal vats is recirculated by means of a
pump at a rate of 80 gallons per minute. This gives an average 5
gallons per minute per square ft. face velocity of liquor passing
through the bag. Makeup water is fed to the bleaching vats from the
rinse vats at a rate of 2000 gallons per hour. This water is pumped
into the bleach vat immediately upstream (i.e. counter to bag
movement) of the first rinse vat. To the makeup water are added 270
lbs./hr. of 10% sodium hypochlorite bleach and 50% caustic soda
solution at the rate required to raise the liquor pH to 10.5.
[0091] The bleach bath liquor is level controlled to a pump that
removes it from the bleach vat which bags first enter. This liquor
is then treated in such a way as to render it acceptable for
disposal and is discharged into the plant waste water stream.
[0092] At this point, the fabric scrap has been bleached to a
uniform CIE brightness of 85 and is ready for dewatering and
drying.
[0093] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *