Introduction
Today, washing
plays an important role in the denim value chain. Lot of customers does not
want to wear and tear their jeans themselves, but want the manufacturer to do
it for them. To achieve this worn look, a lot of different treatments can be
made and different kind of processes and machinery can be used. Some processes
are easy and some are complicated and needs to be carefully controlled. Due to
poor wet and dry rubbing fastness of the indigo dye, every step in the denim
washing process can make a big difference.
 |
| Stone Wash |
STONE WASHING
Stone wash is a
traditional washing process where volcanic rocks or pumice stone are added to
the garments during wash as abradants. Stone washed products will have a worn
look, and are generally a bit puckered at the seams. Usually, stonewashing is
made on indigo dyed garments that easily lose color during abrasion. Often ring
dyed yarns are used, which means that only fibers on the surface have been dyed
and that the core remains uncolored. Stone washing are made with natural and
artificial stones. The artificial stones can be altered according to the wanted
effect and can be made of coal or ceramic. Stone wash causes damage to fibers,
the degree of damage depends on type of stones used and for how long the
garment is stone washed.
ENZYME WASHING
 |
| Enzyme Wash |
Enzyme wash is
a method when garments are washed in a cellulose-based liquid instead of being
washed with stones. The cellulose enzymes are abrading the surface of the
cotton fiber. During strict control, damage on the fibers’ strength and
highlights on seam can be resisted. The same hand can be achieved with enzyme
washing as with stone washing, but in a microscopic level, this process is more
merciful towards the fibers.
There are four
kinds of enzymes for washing:
· Amylase
· Cellulose
· Laccase
· Catalase
Cellulose
enzymes are a mix of enzymes that depolymerize cellulose into glucose and other
lower molecular. In fabric made of cellulose fires, the cellulose enzymes are
by hydrolyze removing the fibers of the surface, even the ones who holds dye. The
neutral enzymes gives less back staining and works best with pH value between
6,0- 8,0 and shows best activity at 55° C. Acid cellulose enzymes works best in
the pH range of 4,5-5,5 and have optimum activity at 50° C.
Enzymes will
attack a specific molecular group. For denim washing, mainly three types of
enzymes are being used. That is neutral, acid and bio polishing enzymes. The
process has to be strictly controlled because of the enzymes sensitivity to
temperature, time and pH. These three parameters highly affect the result and
too big variations can cause damage on the fabric.
After finishing
an enzyme wash, a washing process that rinses the garment has to be done, to
make sure there is no enzyme residue left. This process can be made in
different ways and it will also give the garment a better appearance.
HEAVY STONE WASH
 |
| Heavy Stone Wash |
Heavy stone
wash is a combination of stone washing and enzyme washing. The benefit of heavy
stone wash is a shorter processing time and that almost 50 % less stones and
enzymes are needed. The abrading effect of heavy stone wash depends on the type
of stones, the enzyme type and the duration of the process.
ACID WASHING (ACID WASHED STONE WASH)
 |
| Acid Wash |
Acid washed
garments are pretreated with stones that have been dipped in an oxidant. This
method reduces the physical damage on the garment and reduces the time of
washing. The oxidant will make the indigo molecules oxidate, which will destroy
their ability to reflect blue wavelength. This process is also called dry
bleaching. The size of the stones and the oxidation effect can be adjusted by
demands. By neutralization, the process can be stopped. Acid washing often
gives light parts a light brown shade.
BLEACHING
Bleaching can
be done in several ways, with several bleaching agents:
·
Hydrogen peroxide
·
Potassium permangate
·
Sodium hypochlorite
·
Calcium hypochlorite
Sodium- and
calcium hypochlorite are commonly used for medium to vintage denim looks and
potassium permangate is used for super vintage and light shade looks. Hydrogen
peroxide can be used when a light bleach effect is wanted or if the or if
fabric is Sulphur dyed. Bleaching can cause damage to fibers.
TINTING AND DYING
 |
| Tin Ting |
Tinting and
dying are being done to change hue, cast or tone of indigo. Tinting is when
only parts of the garment are dyed and dying is when the whole garment is dyed.
Generally tinting is used to give denim jeans a worn and vintage look.
SOFTENING PROCESS
When selecting
softeners there are some aspects that must be considered. Softeners may react
with contaminants in high temperatures; this can cause fabric to start
yellowing. Some colors, especially blue and red, are very sensitive towards
softeners, and can after softening change shade. The softeners should be
compatible with wetting agents, dispersing agents and other auxiliaries. Some
softeners can have a solvent effect on certain dye stuffs.