Introduction
Today, washing plays an important role in the denim value chain. Lot of customers do 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.
Today, washing plays an important role in the denim value chain. Lot of customers do 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 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 loses colour during abrasion. Often ringdyed yarns
are used, which means that only fibres on the surface
have been dyed and that the core remains uncoloured. 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 fibres, the degree of damage depends on type of stones used and for how long the garment is stone washed.
have been dyed and that the core remains uncoloured. 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 fibres, the degree of damage depends on type of stones used and for how long the garment is stone washed.
ENZYME WASHING
Enzyme wash is a method when garments
are washed in a cellulase-based liquid instead of being washed with stones. The
cellulase enzymes are abrading the surface of the cotton fibre. During strict
control, damage on the fibres’ 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 fibres.
There
are four kinds of enzymes for washing:
·
Amylase
·
Cellulase
·
Laccase
·
Catalase
Cellulase enzymes are a mix of enzymes
that depolymerise cellulose into glucose and other lower molecular. In fabric
made of cellulose fires, the cellulase enzymes are by hydrolyze removing the
fibres 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 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)
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 fibres.
TINTING AND DYING
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 colours, 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 dyestuffs.
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