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

• Stone wash
• Microsanding

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—

1. Use of cellulase making the seams, hems, and pockets more noticeable
2. Salt pepper effect is color contrast effect.
3. 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:

1. Sandblasting
2. Machine sanding
3. 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-coverings.

Process Flow Chart of Denim Manufacturing | Manufacturing Process of Denim Garments

Flow Chart of Denim Production:

Spinning 
↓ 
Bale Warping 
↓ 
Rope Dyeing 
↓ 
Long Chain Beaming 
↓ 
Sizing 
↓ 
Weaving 
↓ 
Finishing 
↓ 
Inspection & Folding 
↓ 
Packing 
↓ 
Dispatch

Manufacturing of Denim:
The term "Denim" has originated from the city of Nimes in France where "serge de Nimes" was manufactured. Denim is made from a vat dye, the Indigo dye, which is applied to cotton fabric in loosely held form in layers. As far as manufacturing process of denim is concerned, it is similar to that of Grey fabric up to the process of weaving with the only difference that in case of Denim Fabric, it is dyed at the stage of sizing where as in case of Grey Fabric, the decision regarding dyeing stage depends upon the finished product. The details of each process are given below:

Spinning:
The initial stage of denim production is Opening and Blending. Opening begins with baled cotton fiber being separated into small tufts. A blend of cotton fibers is made on each opening line. These bales are selected using USDA High Volume Instrument (HVI) data, and PCCA's unique computer blending software produces optimal yarn strength.

Cotton is delivered by air suction from the Opening and Blending lines, through additional cleaning and blending machines, to the Cards. The major functions of Carding are to remove foreign matter and short fibers, form the cotton into a web and convert the web into a rope-like form known as a sliver.

The drawing process produces a single, uniform sliver from six card slivers. The additional blending, paralleling of fibers and cleaning in this process produces a sliver for Open End and Ring Spinning. For Ring Spinning, however, the sliver must pass through an additional process called Roving.

Cotton Fibers are formed into a yarn by centrifugal action in Open- End Spinning. Individual fibers are laid down in the groove of a fast spinning rotor and twisted into yarn. After the cotton fibers are spun into yarn, the yarn is wound into a large package.

Open End Spinning: 
The Open End Spinning Machines have robots on each side which automatically pieces up (repairs broken ends). On a different track, they have another robot that automatically doffs (removes full packages) and starts up a new package. The size and quality of each yarn end are monitored by the Barco Profile System to ensure uniformity.

Ring Spinning:
In Ring Spinning, the spinning frames receive Roving via a transit system from the roving machine. Yarn is formed from cotton fibers that are twisted together after being drafted by passing between three steel rolls and three rubber rolls. The yarn then is wrapped on a bobbin as it spins on a spindle by use of a traveler. The relationship between roll speeds, traveler speeds and spindle speeds controls the amount of twist in the yarn. Ends down levels and production information are gathered by the Uster Ring Expert System. The spinning frames automatically doff bobbins full of yarn and send them to package winding.

ACG also has the capacity to produce Amsler Open-End yarn, also known as Faux Ring Spun yarn. This technology enables ACG to impart various slub patterns into an Open-End yarn. Denim made from this type of yarn has yarn character and surface interest that cannot be achieved with traditional Open-End yarn.

Fabric Weaving:
a. Grey Yarn on Cones:
Normally yarns received for weaving in cone forms are either from ring spinning or from open end spinning in single or double fold as required. For weaving, yarn used is categorised into:

• Warp yarn
• Weft yarn

Normally for Weaving, yarn used as warp should be sufficiently strong to withstand stress and strains exerted during weaving operations. Hence they are having Count Strength Product(CSP) and further sized to increase its strength. The weft yarn is directly used on weaving machines and in some cases, if required, is rewound also so as to enhance its performance in weaving.

b. Warping on Sectional/ Direct Warping:
The warp yarn is required to be fed into a sheet form to the weaving machines. At warping, the individual cones are put into the creel (the number of cones depends upon fabric construction) and yarn from individual cones is pulled together in sheet form, wound on a barrel called warping beams (for Direct warping) or on weaving beams (for Sectional Warping). Normally if warp sheet is with patterns of different coloured yarns it is processed on sectional warping machine.

c. Sizing of yarn in Set/ Beam to Beam Position:
The object of Sizing is to improve the strength of yarn by chemically binding the fibres with each other and also improve upon its friction resistance capacity by chemically coating the surface of yarn/fibres. Further, number of threads in warpers beam sheet is very less against number of threads required in whole width of fabric. Hence multiplication of sheets by drawing yarns together from many warp beams and again making one sheet is also performed on sizing machine. On sizing, normally, 8-12 % size material on warp thread is applied. This improvement in strength and frictional resistance characteristic of warp yarn is essential because during weaving, yarn has to undergo severe strain & stress as well as frictional operations.

d. Drawing–in:
Weaving is basically interlacement of two sets i.e. warp and weft threads in desired sequence and pattern. To obtain this interlacement, warp yarn sheet is bifurcated & opened in the form of two layers/ sheet and weft thread is inserted between so opened two warp sheets. This operation is called shedding. to perform shedding the warp yarn needs to be passed through heald eyes of the heald shafts, this operation is called as drawing-in.

e. Beam Gaiting or Knotting on Loom:
The drawn weavers beams are fixed on weaving machines, threads are tied and heald shafts are coupled. This operation is called Beam Gaiting. If undrawn warp threads are directly knotted to the threads of finished beams, it is called Knotting. These operations are essential because normally weavers beam can carry only certain length of warp sheet on it and when so woven, whole length is converted to the fabric by weaving machine. Further warp length is required to be fed which can be done by knotting or gaiting other beams on weaving machine.

f. Weaving:
As stated earlier, weaving is interlacing two sets of yarn and making fabric. One set is called warp thread which is in sheet form, the other one is called weft thread which is inserted between two layers of warp sheet by means of a suitable carrier i.e. Shuttle, Projectile, Rapier, Air current, Water current, etc. Depending upon the type of the weaving machines. The different types of technologies available for weaving machines are briefly explained as below:

• Conventional Shuttle Weaving System by Ordinary Looms or Automatic Looms.
• Shuttle less Weaving System by Airjet /Waterjet/Rapier/Projectile

Shuttle loom is a conventional Technology with much less production on account of slow speed and excessive wear and tear of machinery. This shuttle loom technology has now become obsolete. Denim is woven through Shuttle less Weaving System by using 96 ZAX-e Type Tsodakoma Corporation’s Airjet looms or rapier looms or projectile looms. These looms are distinguished by weft insertion method, which is briefly discussed hereunder.

Airjet Looms:
These types of looms adopt the latest development in Weaving Technology where weft insertion is done with the help of compressed air. A very high weft insertion rate up to 1800 metre per minute is achieved. Compared to rapier and projectile looms, these looms are less versatile but are economical and are used in mass textile production unit like denim.

Finishing: 
a. Grey Fabric:
The finally woven fabric or Grey Fabric, as it is popularly called, wound on a cloth roll is taken out from weaving machines at certain intervals and checked on inspection machines for possibilities of any weaving fault. If such faults are seen anywhere in fabric during inspection, certain corrective steps are taken at weaving, warping, sizing, etc so that they can be minimised in subsequent product. This is a quality control exercise.

b. Denim Fabric:
Denim Fabrics woven of 100% cotton would be very strong and durable. Traditionally Blue Denim is warp faced cotton fabric with 3 x 1 twill construction with warp being dyed in a solid colour and weft left un-dyed. The look and quality of the Denim Fabric shall improve after dyeing, the process of which differs from plant to plant. Normally the process of dyeing dictates the technology of Denim manufacturing.

The dyeing for Denim Fabric happens at the sizing stage. Generally there are two most popular methods of dyeing Denim Fabric. They are:

• Rope Dyeing
• Sheet Dyeing

A company can adopt any of the methods. In countries like India Sheet Dyeing Method is commonly used for manufacture of its Denim Fabrics, which has following advantages over Rope Dyeing Method:

• The technology is less capital intensive.
• The technology is a proven one.
• The cost of production is lower.
• The process time is lower.
• The Sheet Dyeing machines are very easy to operate.

The only defect in Sheet dyeing is that their is a problem of center to selvedge shade variation.

c. Sheet Dyeing Process:
This process eliminates a few intermediate processes of the rope dyeing. The yarn sheet is washed with chemicals such as caustic and washing soda and after squeezing the excess water; the yarn sheet is allowed to pass through Dyeing Troughs one time for oxidation and development of dye on yarn. After dyeing, the dyed yarn is washed again with fresh water for two-three times and finalIy squeezed before allowing it to pass through six drying cylinders. The dyed yarn enters the starching device and sizing is done. After sizing, the sized warp beam goes for weaving. After weaving, the woven Denim Fabrics goes for various finishing processes consisting of brushing, singeing, washing, impregnation for dressing and drying. Brushing and singeing should eliminate impurities and help to even the surface of the fabric. Dressing regulates the hand and rigidity of the fabric while compressive shrinking regulates its dimensional stability.

Even today Denim Fabric without Indigo Dyeing is not called authentic Denim. Initially when Denim Fabric entered the fashion market, Denim manufacturers were using Natural Indigo Dye, which was costly and giving a natural finish. Though Synthetic Indigo Dye has gradually replaced Natural Indigo Dye, some unorganised manufacturers still prefer the latter and attract premium after branding them “Natural Dye Used”.

d. Making-Up:
Weaving of fabrics on such multi sizes is not economical, hence a standard width fabrics is then sent to making up. Fabrics are cut into the desired width as per size required on this machine. Denim Fabric and Grey Fabric are thoroughly checked for various types of defects such as:

• Weaving Defects
• Uneven Dyeing
• Bleaching and Dyeing Defect
• Oil Stain
• Patches

Here the final product is categorised quality-wise. The products then found okay are segregated and sent to packaging department whereas defective ones are sent for correction. After inspection, the sets are wrapped with polythene covers and sent for despatch as per buyer’s specifications.

Dispatch:
Rolls and sets so formed and packed as per buyers’ requirements are then sent for final despatches.

Denim Washing | Types of Denim Washing | Process of Denim Washing

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.

Denim washing

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.

Types of Denim Washing:
Denim washing are two types. These are

1. Mechanical washes:

• Stone wash
• Micro sanding

2. Chemical washes:

• Denim bleaching
• Enzyme wash
• Acid wash

Some Important Steps in the Process of Denim Washing:
 1. Pre treatment ( Desizing, Rinsing, Scouring etc)
2. Enzyme or Stone wash
3. Clean up to adjust the desire effect
4. Bleaching
5. Tinting / Dyeing
6. Sand Blasting
7. Softening & Much more…..