Process for forming scrubbed stretch denim fabric

Details Process for forming scrubbed stretch denim fabric Process for forming scrubbed stretch denim fabric

2000-03-30

2003-02-18

Gupta, Yogendra N. (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Natural fiber dyeing

Cellulose textile

C008S149100, C008S494000, C008S532000, C008S637100, C008S653000, C008S916000

Reexamination Certificate

active

06521000

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a process for forming scrubbed stretch denim fabric and particularly relates to a process for forming the fabric employing a simplified finishing technique which is less costly, amenable to higher fabric production rates and has a reduced potential for off-quality fabric.
BACKGROUND
Various types of dyeing and finishing procedures have been used in the past to form scrubbed stretch denim fabric. For example, in U.S. Pat. No. 4,342,565, of common assignee herewith, the disclosure of which is incorporated herein by reference, there is set forth a method for forming fabric of this type, i.e., a weave of cotton and polyester spun blend warp yarns and a fill yarn, preferably formed of stretch polyester, that has been preferably air-textured and entangled or produced by false twisting and heat setting or other known texturing techniques. As set forth in that patent, the scrubbed stretch denim fabric typically includes 388 warp ends woven with the stretch fill yarns in a 2/1 RH twill pattern producing a greige construction width of about 66½ inches with about 59 ends and 35 picks per inch and a finished construction width of about 58 inches with 68 ends and 39 picks per inch.
Over the years, that process has been modified to form essentially the same scrubbed stretch denim fabric construction. The process disclosed in U.S. Pat. No. 4,342,565, modified as currently employed to produce commercial scrubbed stretch denim fabric prior to the present invention is described with reference to
FIG. 1
herein. The current methods have altered the patented process of U.S. Pat. No. 4,342,565 in many respects, including eliminating hot dyeing. The currently employed method of dyeing the yarns used to form present-day commercial scrubbed stretch denim fabric commences as illustrated in
FIG. 1
, with an initial scouring of the yarns using a scouring bath
10
similarly as set forth in U.S. Pat. No. 4,342,565 but with a different scouring solution. The current scouring bath is an aqueous solution comprised of 55 pounds of Sedgequest EDTA-100; 168 pounds of Caustic (50%); 52 pounds of Penetrant TER; and 3 pounds of a Defoamer 2403 and sufficient water to bring the total volume to 900 gallons. The yarns are passed through the dyeing process including the a scouring bath at a rate of about 38 yards per minute (YPM) and passed through the scouring bath
10
at a preferred scouring temperature of 190° F. for 15 to 25 seconds. Following scouring, the yarns are rinsed in a series of baths
12
and
14
of hot water ranging in temperature from 160° F. down to 80° F, to remove natural oils, waxes or other additives from prior textile operations. The final rinsing is in a cold wash bath
16
at approximately 90° F.
In contrast to the patented process set forth in U.S. Pat. No. 4,342,565, the current processing provides for dyeing wet on wet yarns. This is accomplished by increasing the squeeze roll pressure on the last wash bath prior to dyeing to maximize the wet pick-up potential. Thus, instead of passing the yarns over drying cans prior to dyeing as in the patented process, the yarns are introduced directly into the indigo dye bath. The dye bath is maintained at a temperature in a range of about 70° to 90° and preferably 85° F. The currently employed indigo dye bath is preferably prepared in accordance with the following example wherein the indigo stock mix includes 171 pounds of caustic (50%), 23 pounds of dry hydrosulfite, 630 pounds of Indigo paste (20%), and 13 pounds of Penetrant TER and sufficient cold water to bring the total volume to 250 gallons. The hydro portion of the dye bath mix comprises 41 pounds of dry hydrosulfite and 44 pounds of caustic (50%) and sufficient cold water to bring the total volume of the hydro portion to 200 gallons. The hydro solution is mixed at a temperature of approximately 70° F. and is mixed with the indigo stock mix, the combination of the indigo stock mix and hydro mix being maintained at an ambient temperature in a range of 70°-90° F. and preferably approximately 85° in the dye bath.
In the current method, the warp yarns make three passes through the dye baths indicated at
18
,
20
and
22
in
FIG. 1
, with the warp yarn remaining immersed in each bath approximately 5 to 15 seconds and being skyed after each pass as discussed below. The immersion time of approximately 5 to 15 seconds is sufficient to have the dye solution penetrate the yarn. The reduced indigo, caustic and hydro mixture is continuously fed to the indigo dye baths to maintain a substantially constant indigo concentration level and to simultaneously maintain a high oxidation reduction potential of approximately 960 mv. In contrast to the patented process, the current process is to dye the yarns at normal temperatures. ranging from 70-90° F. and preferably about 85° F.
The yarns emerging from each dye bath are passed through the atmosphere or “skyed” for approximately one minute to complete reoxidizing the indigo. The skying following each dye bath
18
,
20
and
22
is indicated at
19
,
21
and
23
, respectively, in FIG.
1
. Subsequent to the final skying at
23
, the warp yarn is washed in 3-7 successive running washes ranging in temperatures from 80° F. to 140° F. as indicated at
26
,
28
,
30
,
32
,
34
and
36
in FIG.
1
. The preferred temperatures for the cold washes are indicated in FIG.
1
. Subsequent to the cold washing of the dyed yarns, the yarns are passed through a softener mix maintained at a temperature of approximately 125° F. The softener mix, as currently employed, comprises 190 pounds of Indilube C-20 in an aqueous mixture to obtain a total volume of approximately 400 gallons. The yarns are then dried over a series of dry cans
40
,
42
,
44
,
46
,
48
,
50
and
52
as illustrated in FIG.
1
. While the dyeing techniques currently used to dye yarns for forming commercial scrubbed stretch denim fabric are dissimilar in the foregoing respects from the dyeing technique disclosed in U.S. Pat. No. 4,342,565, the resulting textile product dyed by the current procedure has a similar indigo dye penetration deep into the fiber bundle without the yarns exhibiting the usual ring-dyed effect occurring in regular indigo dyeing.
Subsequent to dyeing the warp yarns, the dyed warp yarns and stretch fill yarns are woven to form the denim fabric and thereafter finished to produce the scrubbed appearance, proper hand and final finished stretch characteristics desired for the denim fabric. In the current finishing process as illustrated in
FIG. 1
, the woven fabric is first brushed and passed through a singer, as indicated at
54
and
56
, respectively. Before passing the woven fabric through open width wash boxes as in the patented process, the current process passes the woven yarn through a preparation pad box wherein the fabric travels over a series of immersed rolls, and subsequently passed through a squeeze roll. This helps develop stretch by applying wet heat to reduce fabric width. A scouring agent is employed in the preparation pad box
58
to remove loose unfixed dye on the fabric. The preparation pad box includes a bath of 12 pounds Protowet 5917 and two pounds Defoamer 2403 in a water solution of approximately 875 gallons. Thus, the aqueous solution contains 0.17% of scouring agent.
As in the prior patented process, the woven fabric is then passed through a series of open width wash boxes schematically indicated at 60 for washing the fabric at temperatures in a range of 130-160° F. These temperatures are lower than the corresponding processing temperatures set forth in the patented process. The wash boxes are maintained with a pH of about 10 or 11 and the fabric moves at approximately 65 yards per minute through the wash boxes. Subsequent to the wash boxes, the fabric is passed over a series of drying cans
62
with steam supplied the cans in a range of 30 to 60 pounds per square inch to provide a fabric moisture content of about 6-8%. Current industry standards indicate that to develop filling stretch, hot water

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