Fabric and garment finishing :
Basic washes in denim fabric
THE HISTORY
OF DENIMS
A popular
conception of the etymology of the word denim is that it is a contraction or
derivative of the French term, serge de Nmes. Denim was traditionally colored
blue with indigo dye to make blue “jeans,” though “jean” then denoted a
different, lighter cotton textile; the contemporary use of jean comes from the
French word for Genoa, Italy (Gnes), from which the first denim trousers were
made.
A similarly
woven traditional American cotton textile is the diagonal warp-striped hickory
cloth that was once associated with railroad mens overalls, in which blue or
black contrasting with undyed white threads form the woven pattern. Hickory
cloth was characterized as being as rugged as hickory woodnot to mention the
fact that it was deemed to be worn mainly by “hicks”although neither may be the
origin of that term [from a nickname for "Richard"]. Records of a
group of New Yorkers headed for the California gold fields in 1849 show that
they took along four “hickory shirts” apiece. Hickory cloth would later furnish
the material for some “fatigue” pantaloons and shirts in the American Civil
War.
INTRODUCTION
Denim is a rugged cotton twill
textile, in which the weft passes under two (twi- “double”) or more warp
fibers, producing the familiar diagonal ribbing identifiable on the reverse of
the fabric.
DENIM
WASHING
Denim
washing is the aesthetic finish given to the denim fabric to enhance the appeal
and to provide strength.
Dry denim,
as opposed to washed denim, is a denim fabric that is not washed after being
dyed during its production.
Much of the
appeal of dry denim lies in the fact that with time the fabric will fade in a
manner similar to that which artificially distressed denim attempts to
replicate. With dry denim, however, such fading is affected by the body of the
person who wears the jeans and the activities of their daily life. This creates
what many feel to be a more natural, unique look than pre-distressed denim.
DENIM WASHES
ARE OF TWO TYPES:
1. Mechanical washes
2. Chemical
washes
- Denim bleaching
- Enzyme wash
- Acid wash
CHEMICAL
WASHES
Denim bleach
In this
process a strong oxidative bleaching agent such as sodium hypochlorite or KMnO4
is added during the washing with or without stone addition.
Discoloration
produced is usually more apparent depending on strength of the bleach liquor
quantity, temperature and treatment time.
It is
preferable to have strong bleach with short treatment time.
Care should
be taken for the bleached goods so that they should be adequately antichlored
or after washed with peroxide to minimize yellowing. Materials should be
carefully sorted before processing for color uniformity.
Process cycle:
Limitations:
- Process is
difficult to control i.e. difficult to reach the same level of bleaching in
repeated runs.
- When desired level of bleaching
reached the time span available to stop the bleaching is very narrow. Due
to harshness of chemical, it may cause damage to cellulose resulting in
severe strength losses and/or breaks or pinholes at the seam, pocket, etc.
- Harmful to human health and
causes corrosion to stainless steel.
- Required antichlor treatment.
Problem of
yellowing is very frequent due to residual chlorine.
Chlorinated
organic substances occur as abundant products in bleaching, and pass into the
effluent where they cause severe environmental pollution.
EnzymeWash
It is
environmentally friendly wash. It involves the Application of organic enzymes
that eat away at the fabric, i.e. the cellulose.
When the
desired color is achieved, the enzymes can be stopped by changing the
alkalinity of the bath or its temperature. Post treatment includes final
rinsing and softening cycle. The effects produced by the cellulose enzyme are—
- Use of cellulase making the
seams, hems, and pockets more noticeable
- Salt pepper effect is color
contrast effect.
- Faded garment with acid
cellulase enzyme provides less color contrast in proportion to garment
washed with neutral cellulase enzymes.
Garment load
size of the machine is 35-40 jeans per machine and it cannot be overloaded.
Acid wash
It is done
by tumbling the garments with pumice stones presoaked in a solution of sodium
hypochlorite or potassium permanganate for localized bleaching resulting in a
non uniform sharp blue/white contrast.
In this wash
the color contrast of the denim fabric can be enhanced by optical brightening.
The advantage of this process is that it saves water as addition of water is
not required.
Process
cycle
Limitations of acid wash:
- Acid
washed, indigo dyed denim has a tendency to yellow after wet processing.
- The major
cause is residual manganese due to incomplete neutralization, washing or
rinsing.
Remedy:
- Manganese is effectively
removed during laundering with addition of ethelene-diamine-tetra-acetic
acid as chelating agent.
- Acid washing jeans avoided some
of problems of stone wash, but came with added dangers, expenses, and
pollution.
MECHANICAL
WASHES
Stone wash:
In the
process of stone washing, freshly dyed jeans are loaded into large washing
machines and tumbled with pumice stones to achieve a soft hand and desirable
look.
Variations
in composition, hardness, size shape and porosity make these stones
multifunctional. The process is quite expensive and requires high capital
investment.
Pumice
stones give the additional effect of a faded or worn look as it abrades the
surface of the jeans like sandpaper, removing some dye particles from the
surfaces of the yarn.
Process cycle:
Selection of
stone
Stone should
be selected of the proper hardness, shape, and size for the particular end
product. It should be noted that large, hard stones last longer and may be
suited for heavy weight fabrics only.
Smaller,
softer stones would be used for light weight fabrics and more delicate items.
Stone wt.
/fabric wt. = 0.5 to 3 /1
It depends
on the degree of abrasion needed to achieve the desired result. Stones can be
reused until they completely disintegrate or washed down the drain.
Problems caused by stones:
- Damage to wash machineries and
garment due to stone to machine and machine to stone abrasion
- Increase in labor to remove
dust from finished garments.
- Water pollution during disposal
of used liquor.
- Back staining and re
deposition.
Back
staining or Re-deposition:
The dye
removed from denim material after the treatment with cellulose or by a
conventional washing process may cause “back staining or “redeposition.
Re-coloration of blue threads and blue coloration of white threads, resulting
in less contrast between blue and white threads.
Remedy of
back staining —
- Adding dispersion/suspension
agent to wash cycle.
- Intermediate replacement of
wash liquor.
- Using alkaline detergent like
sodium per borate with optical brightener as after wash.
Limitations
of stone washing:
- Quality of the abrasion process
is difficult to control Outcome of a load of jeans is never uniform,
little percentage always getting ruined by too much abrasion.
- The process is non-selective.
- Metal buttons and rivets on the
jeans in the washing machines get abraded.
- This reduces quality of the
products and life of equipment, and increases production costs.
- Stones may turn into powder
during the process of making the garment grayish in color and rough too
- Provides rougher feel than
enzyme wash
- Stone may lead the harm to the
machine parts
Microsanding
There are 3
ways for this technique:
- Sandblasting
- Machine sanding
- Hand sanding or hand brushing
Used in various ways:
- Flat surfaces (tables, ironing
boards)
- On the dummy (inflatable
dummies, sometimes standing, sometimes flat, sometimes ‘seated’)
- Various templates can be used
to create a 3D effect.
SAND BLASTING
Sand
blasting technique is based on blasting an abrasive material in granular,
powdered or other form through a nozzle at very high speed and pressure onto
specific areas of the garment surface to be treated to give the desired
distressed/ abraded/used look.
- It is purely mechanical
process, not using any chemicals.
- It is a water free process
therefore no drying required.
- Variety of distressed or
abraded looks possible.
- Any number of designs could be
created by special techniques.
WHISKERING
- Also known as Cat’s Whiskers
- Crease lines around the
crotch.
- Industrially done with laser,
sandblasting, machine sanding, hand sanding and abrasive rods.
- Also used for ‘knee whiskers’
(whiskers on the sides of knees) and ‘honeycombs’ (crease marks on the
back of the knee)
Other
chemical washes:
- Rinse wash
- Cellulase wash
- Ozone fading
- Snow wash
- Salt water denim
- Flat finish
- Over dye
- Sun washing
- Super dark stone
RINSE WASH
- Chemically
bleaching jeans so that the color fades away
- Breaks down the fibers of jeans
and creates white streaks or spots on denim
- Gives a unique rugged look,
also called snow wash
- Earlier involved the use of
pumice stone
- Presently process involves
spraying chemical and removing it immediately
- Come in colors like blue,
black, green, brown, grey etc.
CELLULASE
WASH
- This is done to achieve a wash
down appearance without the use of stones or with reduced quantities of
stones.
- Cellulase enzymes are selective
only to the cellulose and will not degrade starch.
- Under certain conditions, their
ability to react with cellulose (cotton) will result in surface fiber
removal (weight loss).
- This will give the garments a
washed appearance and soft hand.
Factors
influencing cellulase performance
- pH
- Temperature
- Time
- Dose
- Mechanical action
OZONE FADING
- By using this technique, the
garment can be bleached.
- Bleaching of denim garment is
done in washing machine with ozone dissolved in water.
- Denim garments can also be
bleached or faded by using ozone gas in closed chamber.
- In the presence of UV light,
there is an interaction between the hydrocarbons, oxides of nitrogen and
oxygen that causes release of ozone.
- Indigo dyestuff tends to fade
or turn yellow due to ozone reaction.
The
advantages associated with this process are:
- Color removal is possible
without losing strength.
- This method is very simple and
environmentally friendly because after laundering, ozonized water can
easily be deozonized by UV radiation.
FLAT FINISH
It is a
special process done to impart fabric with an even wash down effect and very
clean surface. Originally liquid ammonia was used, but now use mercerization
plus calendering processes to achieve the flat surface.
Mercerization
swells up the cotton fibers and allows the calendering to press flat the
surface.
They
consider this as an imitation process to the use of ammonia, which is toxic and
not allowed in commercial use in most countries
OVERDYE
- Dyeing over the fabric or jeans
to add another tone of color
- Most often used is a ‘yellowy’
overdye to create a ‘dirty’ look
- Also can be applied with spray
gun or paintbrush for local coloring
SUNWASHING
- A very light shade by bleaching
and stoning
- Looks as if the sun faded the
fabric
SUPER DARK
STONE
- Commercial term for an extra
dark indigo color
- Results from a double-dyeing
technique
SNOW WASH
DENIM
Denim
treated with a variation of acid wash that imparts bright white highlights.
QUICK WASH
DENIM
- Aims at minimizing wash cycle
time
- Results in more economical
washes and solving many other washing problems faced by launderes during
fashion wash cycles
- The yarns are ring dyed using
indigo giving 25 to 30% less fixed dye to obtain a given shade
- During wash cycle,indigo dye
can be removed quickly,giving washed look
Advantages of quick wash denim
1. Streaks
develop in garments after washing process due to differences in dye
concentration of denim fabrics are avoided using a modified alkali-ph
controlled system giving uniformity of shade.
2. Amount of
indigo dye required is less thus making it an economical process
3. Time
required for washing is 20-30% less than that required for conventional denim.
4. Lesser
enzymes and oxidising agent used
5.
Environment friendly process
6. Back
staining is minimised due to less concentration of of indigo dye in the wash
liqour.
Other
Mechanical washing
- Whiskering
- Shot gun denim
- Water jet fading
- Super stone wash
- Ice wash
- Thermo denim
- Laser technology finish
WATERJET
FADING
- Hydrojet treatment is used for
enhancing the surface finish, texture, durability of denim garment.
- Hydroject treatment involves
exposing one or both surfaces of the garment through hydrojet nozzles.
- The degree of colour washout,
clarity of patterns, and softness of the resulting fabric are related to
the type of dye in the fabric and the amount and manner of fluid impact
energy applied to the fabric.
- As this process is not involved
with any chemical, it is pollution free.
LASER
TECHNOLOGY
- It is a computer controlled
process for denim fading.
- This technique enables patterns
to be created such as lines and/or dots, images, text or even pictures.
- It is water free fading of
denim.
- Being an automatic system,
chances of human error are slim.
- Also called spray painting in
denims.
- This technique has relatively
high cost.
SUPER
STONEWASH
- Prolonged stonewashing, up to
six hours or more.
ICE WASH
- Ice washing in denim fabrics is
done to remove more than half the dye during washing
THERMO-DENIM
- Also called double denim. A
lightweight fabric (either plain, fancy or colored) is glued to the denim.
The glue comes off after washing and the trousers look like they’ve been
lined
VINTAGE
- Applies heavy stonewashing or a
cellulose enzyme wash, with or without bleach
- Gives an old and worn look
CHEMICALS ON
DENIMS
1. Bleach fast Indigo
- Value addition to denim
- Retains indigo on certain parts
- Kind of resist effect
- Chemical applied by brush,
cured at 150C
- Ex. Indigofix AXN
2.
Anti-depositing agent
- Prevents back staining of
fabric by loose indigo during washing
- Improves contrast in denim
- Used in stone wash step
3. Dye
stuffs with softener
- - To carry dyeing and softening
in one step
- - Soft and supple hand
- - Saves time, money and energy
as added to final rinse
- - Gives used and worn out
effect
4. Anti
creasing agent
- Provides fabric to fabric
lubrication
- Prevents formation of crack
marks and streaks
- Minimizes abrasion and gives
strength
5. Wrinkle
formation
- Creating smooth and permanent
wrinkle
- Cross linking concept
- Ex. DMDHEU
- White pigment
- Can be applied by brush, spray
or screen
- Then cured at 150C
- Washed and treated with
softener
6. White
pigment
- Can be applied by brush, spray
or screen
- Then cured at 150C
- Washed and treated with
softener
CONCLUSION
Denim is
unique in its singular connection with one colour. The warp yarn is
traditionally dyed with the blue pigment obtained from indigo dye. Until the
introduction of synthetic dyes, at the end of the 19th century, indigo was the
most significant natural dye known to mankind, linked with practical fabrics
and work clothing. The durability of indigo as a color and it’s darkness of
tone made it a good choice, when frequent washing was not possible.
The old mass
market has segmented, fragmented, shattered into a multitude of mini, micro and
niche markets. The last generation has a vast quantity of brands to choose
from, a different perception of the cult value of owning small insider labels
and a fanatical loyalty only to what’s hot on a daily basis.
Freed of all
social and creative restrictions, denim is assuming any number of disguises and
contexts to be worn in and has broken through almost any limitation on price.
It can also be found in home collections, appearing in cushions, bed spreads
and furniture-coverin
