PROBLEMS & THEEIR REMEDIES IN POLYSTER PROCESSING

Problems and Their Remedies in Polyester Processing-

 

 

 

 

Introduction

 

The estimated polyester fibre production, in 2007, was 34 million tons (approx)-39.7% of the whole textile
fibre production-while, cotton production was 28 million tons (approx) and other cellulosic fibres, 2.8 million
tons (approx). On a positive note, polyester fibres are estimated to grow by 5% annually, even as other
textile fibres stagnate or decrease.

 

What is PET?

 

The development of fibres from polyester have come a full circle since scientists at ICI, UK, first produced
dimethyl terephthalate from ethylene glycol and terephthalic acid. Subsequent years saw the arrival of this
new fibre in the market, chemically known as polyethylene terephthalate (PET).

 

Independent of this research, DuPont (US) and Hoechst (Germany) also developed this synthetic fibre. By
today's standards, it is the most versatile synthetic fibre ever invented. It lends itself beautifully alone, as a
textile fibre, or as blends with cotton, viscose, polynosic, linen, silk, wool or hemp. The chief characteristics
of this fibre include:

 

• Good crease recovery
• Good shape retention
• High bulking capacity
• Good abrasion
• Tear resistance
• Good dye ability
• Acceptable moisture absorption
• No strength loss during wetting and other chemical treatments
• Resistance to microorganism, insects, mildew, etc.

 

Structure and modifications

 

Mainly manufacture by the direct reaction of terephthalic acid and ethylene glycol, polyester is devoid of
functional groups.

 

Polyester modifications are made to alter the inner structure of the fibre. These modifications are physical,
using special methods, or they contain copolymers or different chemical components, giving the desired end
results like low pilling, dyeing behavior to anionic and cationic dyes, etc. An interesting modification is the
process known as ‘texturising’, where the molten fibre is first stretched and then cooled. It gives the fabric a
luxurious bulkiness, softness and extra shine.

 

Various types of additions and modification also affect the performance of the fibre/ fabric. For example,
delustering agents (usually titanium dioxide) results in dull polyester, while adding optical whitener to the
fibre before spinning produces white fibre.

 

Physical Properties

 

• Density: 1.38 - 1.5
• Melting point: 252 - 256οC
• Softening point: 230 - 250οC
• Glass transition temperature: 68οC

 

Drawbacks

 

The major drawback of the low moisture regain polyester fibres is its wearing comfort. Hence, 67/ 33%
blends with cotton result in excellent fabrics having the best properties of both the fibres. Another
disadvantage is that oils, fats, grease, etc. can easily soil polyester fabrics because of the electrostatic
charge build up and the fibres tend to pill. Hence, adding a singeing process takes care of this problem by
burning off the surface fibre.

 

Dream come true

 

In the 90’s the polyester micro fibre was a commercial breakthrough in the world of synthetic textiles. A
polyester fibre of exceptional soft feel, comfort, and rich appearance, was a synthetic fibre technologist’s
dream. Micro fibres made it a reality.

 

What is so special about micro fibre?

 

• Excellent softness
• High drape
• Silky handle
• Good breath ability
• Super comfort
• Rich appearance

 

Thus its use is rapidly growing in the fashion apparel sector as well as the technical textile sector – which
itself is growing at rate of 35% in India. Considering these trends and the versatile uses of polyester
microfilament fabrics, studying aspects of wet processing and problems in coloration of microfilament textiles
is worthwhile.

 

Right first time

 

In textile wet processing problems and their remedies are very important. As a ‘wrong first time’ is followed
by harsh consequences like:

 

• Extended processing time
• Substandard fabric
• Extra cost
• Additional energy
• Late delivery
• Late delivery of following batches

 

 Preparatory chemical processing for polyester

 

 

Singeing

 

Singeing is a pretreatment for PET-cellulosic blend fabrics (not 100% PET fabric). The modern gas singeing machines have efficient and computer controlled burners, which can control the width, height, angle and intensity of the flames.

 

Problems encountered:

• Any uneven heat transfer is liable to cause variations in the setting of PET fibres, resulting in uneven, dyeing of fabric.
• In singeing protruding PET fibres tend to form globules, which are difficult to remove.
• The globules dye deeper shade than the original fibre when dyeing is carried out by exhaust method.

 

Remedies:

 

• Singeing as a pretreatment should only be done if the continuous thermosol method is used for dyeing.
• Singeing effect, if one or more passages are given, can reduce the pilling effect on the fabric. Leading to better usage and thus in such cases singeing acts as post treatment machine.

Setting of polyester

 

In order to achieve good shape retention and prevent running creases from marking during wet processing, PET fibres and their blends must be stabilised. In other words, tension within the individual fibres and in the fabric is leveled out by relaxation. Heat setting of PET is carried out at 180 C, to ensure 0% residual shrinkage (natural shrinkage) and completion of primary crystallization.

 

Problems:

 

• Measurement of surface temperature of fabric
• Speed uniformity in machine
• Non-uniformity in setting effects for large run of fabrics
• Incomplete removal of residual shrinkage (0% shrinkage never achieved)
• Excessive shrinkage causes problems in subsequent processes

 Remedies:

 

•  Accurate and precise measurement of fabric surface temperature using infrared sensing thermometers
•  Measuring residual shrinkage in lab (should not be more than 0.5%)
•  Achieving precise relaxation of fabric by over feed arrangement
•  Using modern hot air stenters for accurate speed adjustment, air humidity measurement and overfeed

 Chemical preparation

 

 Processing aids are applied during sizing of microfilament yarns in order to help and protect the delicate polymer fabric during processing. The common feature of all washing processes is the exchange of substances in an aqueous media.

 

 Problems:

•  Temperature variations in the batch cause variations in the degree of bleaching
•  Poor temperature control can cause fibre tendering
•  Variations in reaction time between ends of the cloth on the batch can cause ‘tailing’ in dyeing
•  Efficient and optimal removal of sizes and other processing aids
•  Creasing and abrasion marks in the fabric during chemical pretreatments

 Remedies:

• To minimize creasing, it is important to control shrinkage of the fabric i.e. relaxation should occur under minimum tension
• To reduce creasing, use of suitable lubricating agent is recommended
• Latest Harish JT10 type of jiggers and lately atmospheric pressure jiggers, it is possible to have heat efficiency and liquor spray and D.C. motor drives for uniform treatments
• Variations of these with micro process controls and uniform speeds from beginning to end and with HTHP arrangements can be used for this process
•  For the removal of large amounts of oils or fats like oils and spin finishes, pre-cleaning with organic solvents (perchloroethylene) has established itself
• Weight reduction process carried out by caustic soda of concentration 22-25% by weight at elevated temperature of 90 - 95°C under controlled time gives polyester a silk like appearance adapted successfully in India

Printing

  

Printing of polyester is a specialized subject that needs elaborate study. Polyester can be printed with the following class of dyestuffs:

•  Indigo sol colours
•  Pigment dyes
•  Disperse dyes

 Disperse printing of polyester consists of following fundamental principles:

•  Thickener-acid stable
•  Disperse dyes
•  An acid donor or catalyst
• An auxiliary to enhance the dye uptake as and when required

 The methods of fixation after printing and drying are:

 

• Pressure steam fixation method
• High temperature steam fixation method
• Thermo fixation method

Thickening agent is the most important component of the printing paste and it should be cost effective. The fact is that since the printing paste is acidic the thickener should have very good stability in the pH range of 2-5 for long time. The most favoured thickener the world over is guar gum. Others include:

• Modified guar gum
• Carboxyl methyl cellulose
• Sodium alginate
•  Synthetic thickeners based on polymeric organic compounds

The disperse dyes usually become dull under alkaline conditions. To improve this, the pH of the print paste is controlled to pH of 4.5-5 by addition of citric or tartaric acid – the more common being citric acid. However, tartaric acid is selective in some real cases where the acidic conditions are more stable than citric acid.

 

Problems:

 

• Splashing printing paste during printing due to vibration of blotting paper
• Sticking and threading property of gum when screen is lifted causes sharp lines losing their sharpness
• Yellowing and uneven prints of the printed fabric cloth causing poor sharpness, brightness, colour value
• Bleeding at the time of printing and steaming, caused by the use of excess urea. Coarse screen mesh and excess dyestuffs may cause bleeding as well
• Changing tone due to high time lapse between printing and drying. improper heating in the ager also results in tone variation due to uneven diffusion of disperse dyes
• Hallowing/ mark off due to sublimation of disperse dyes having low sublimation fastness
• Changing colour value due to incompatibility of dye combinations. The presence of impurities in water like calcium, magnesium and iron forms a complex with the dyestuffs, lowering the colour value and giving a dull effect
• Staining during after treatment if proper sequence of rinsing is not followed, because superfluous disperses dyes get re-deposited on the unprinted cloth during hot water rinsing

Remedies:

 

• Proper viscosity of print paste. Guar gum and its percentage with proper cooking method will eliminate the splashing problem. A gum paste having higher solid content and certain plasticity is recommended
• Fabric should be free from auxiliaries like size, coning oil, non-ionic emulsifiers and cotton impurities, to eliminate the problem of yellowing and uneven prints of printed fabric
• Selecting suitable thickener, moderate strength of the dyestuffs, appropriate dosage and small motifs in printing excludes bleeding. Low viscosity of paste may cause bleeding
• Tone change can be eliminated by uniform heating and quick drying. Auxiliaries, like print developer TX, have a synergistic action on the different types of dyes used in mixing and brings about synchronization of diffusion rates of individual dyes
• Hallowing/ mark off can be negated by selecting proper dyes and good quality wrapper (cotton wrapper) for pressure aging
• Colour value change can be barred by maintaining appropriate pH of 5-6. Compatibility of dyes i.e. having diffusion temperature in the same range is selected. Use of sequestering agent in print paste is important or else usage of soft water is emphasized
• After-treatment staining is reduced by following the sequence of: Cold wash 􀃆 Reduction 􀃆 Hot water 􀃆 Soaping 􀃆 Clearing􀃆Rinsing
• Using a good auxiliary like catalyst PC helps in removal and destroying unfixed superfluous disperse dyes and also helps in breaking baked-dried film of printing gum faster  

Washing

 

 Good printing can be spoiled by bad or improper washing techniques. Essentially, the best washing sequence has to follow the following steps:

 

• Soak the printed fabric well to swell the gum of the print paste for easy removal
• Remove the swollen gum by an efficient washing arrangement in the open soaper or winches
• Continue washing in 2-3 compartments in cold and agitating conditions, till the wash water is free from contaminated colours
• Add 2-3gpl of good quality detergent with dispersing functions-0.5-1gpl caustic soda, 1-2gpl sodium hydrosulphite-to remove all unfixed dyestuffs efficiently
• Treatment with 2-3gpl detergent and 1-2gpl of soda ash at boil, in two compartments followed by drying in drying ranges after hot wash.  

INDIGO CHEMISTERY

Indigo is a powder, insoluble in water, with a melting point higher than 300C. It absorbs light in the yellow region of the spectrum (maximum at 602 nm), which gives it its intense blue colour. The indigo molecule is relatively small with molecular weight of 262.27 atomic units of mass. In the molecular models illustrated on this page carbon is shown in grey, oxygen in bright red, nitrogen in blue, bromine in deep red and hydrogen in white. Conventionally, hydrogen atoms are not shown in diagrams, as their position and number is implied by the valence of carbon and other atoms, to which they are attached. Figures 1, and 2 show indigo molecules in this abbreviated form. Indigo is derived from two indoxyl rings joined at position 7 on each ring. Derivatives, where hydrogen substitutions in positions 6,6' for bromine or in positions 5,5' for SO3.Na result in related dye molecules giving purple or carmine colour.


Blue indigo does not react with and will not bind chemically to fabric fibres, as most dyestuffs do. However, in the presence of a reducing agent (e.g. alkaline pH) it can undergo a two stage reduction (gain of electrons) on the oxygen atoms at positions 3 and 3' to a soluble form. Oxidation - reduction occurs when electrons are transferred from a donor (oxidising agent) to an acceptor (reducing agent). An indigo dye vat provides a reducing environment to keep the dye in solution. In this form indigo will penetrate and adhere to fabric fibres. When the fabric is removed from the vat in-situ oxidation of indigo occurs and the oxidation traps the molecule in the matrix of the fabric. This process is dramatic to watch because the soluble form of indigo is yellow and, as it contacts air, oxidation occurs that changes the colour to deep blue in a few moments. A single step dyeing process such as the one described here does not require an alkaline dye environment because the dye is disposed of once oxidised and will not need to be re-used.


Oxidation of indigo to its blue insoluble form is facilitated by exposure to air, heat and strong light. Once oxidised, indigo molecules are trapped inside the fibres of the surface, to which they were applied. Fading occurs as the small molecules drop out of the cellulose or protein bundles of the fabric and the three dimensional structure that holds them. Wear and flexing promote this loss of indigo dye.


By the end of the 19th century the demand for blue indigo dye began to exceed the supply available from the indigo plantations of India. The 1905 Nobel Prize in Chemistry was awarded the German chemist Johann Friedrich Wilhelm Adolf von Baeyer the first person to determine the molecular structure for indigo.

Safety Notes: Irritant, do not inhale.

Tyrian Purple



Tyrian Purple, also known as Royal purple, was made from a secretion gathered from various marine molluscs, such as Murex trunculus and Murex brandaris. The dye is costly to harvest, requiring 12,000 molluscs for just 1.4 grams of pigment, thus in many cultures purple was reserved only for the use of the noble classes that could afford it. Tyrian Purple can also be used to make a blue dye but the plant form of indigo is much cheaper and the colour identical.

Figure 2. 6,6'-dibromoindigo

Tyrian Purple, is so closely related to indigo that the two molecules are almost identical. The chemical name for Tyrian Purple is 6,6'-dibromoindigo. The difference between the two dye molecules is the substitution of two hydrogen atoms for two bromines, as shown in the diagram below.

Figure 3. Hydrogen Substitution


Understanding pH in the Indigo Dye Vat


An indigo dye vat provides a reducing environment to keeping the indigo dye in solution. In this form indigo will penetrate and adhere to fabric fibres. A natural fermenting indigo dye vat operates at about pH 9.5. The efficiency of a vat can be improved with the use of a very strong reducing agent like sodium hydroxide. Ancient Blue Crystal Indigo is a ready made dye vat in a desiccated form. When water is added the instant dye vat is ready to be used. The pH of this type of dye vat can be very high indeed and could cause skin damage. The diagram below demonstrates how pH can be reduced using dilution and how much dilution is required for one unit reduction in the pH.

Figure 1. Two volume measurements are required 50 and 500 ml.

Figure 2. One gram of freeze dried indigo vat is placed in the 50ml measure and topped up with warm water. pH = 13

Figure 3. The first dilution is added to 450 ml of water. pH = 12

Figure 4. Take 50ml from the large cup and add this to 450ml of water. pH = 11

Figure 5. Take 50ml from the large cup and add this to 450ml of water. pH = 10

Figure 6. Take 50ml from the large cup and add this to 450ml of water. pH = 9

DENIM BRAND

Here we are listing about 50 Top and the Best Denim Brands around the world. These brands are from different countries – from USA , Japan, UK, Italy, Scandinavia etc.

The brand names have links on them which will take you to their websites.

Denim Brands from many countries including Japan, Italy, France, Sweden, Australia, USA, Netherland etc are mentioned. Below the table you will find the details on some of the important brands – segregated country wise.


Best Denim Brands Worldwide – Europe/ Americas/Asia

Japanese Denim Brands

1. 45rpm : 45rpm is very cautious about the fabrics it uses and has an exclusive deal with its mill, ensuring one-of-a-kind materials. The company’s denims are made from both Zimbabwe cotton and Suvin hybrid cotton,
2. Edwin : Founded in 1969 by Edwin Company mainly focused on jeans manufacture. Brad Pitt is an official spokesperson and model for the brand, and appears in many of its advertisements.
3. Evisu : Founded in 1991 by Hidehiko Yamane. Yamane-san was trained as a tailor but his love for vintage denimn and his disappointment with the mass-produced modern versions led him firstly to business of vintage clothing import business and later to start putting together the elements required to reproduce vintage-style jeans. The initial production was 14 pairs of jeans a day !
4. Iron Heart : The denim is made in Japan out of the highest quality, long fibre cotton. These long fibres allow the individual cotton threads to be spun less tightly than is normal. The result is a surprisingly soft feel to this ultra-heavy denim.
5. PRPS : Made from Zimbabwe Organic Cotton, the denim dream of the founder of Akademics and ex-Nike designer, PRPS defines perfection in today’s over saturated denim market.
6. Samurai : Founded in 1997,their collection exists of various models of unwashed denim. All Samurai jeans,uses 100% pure indigo with no fillers, and use the maximum amount of indigo that the yarn can hold. Samurai has also maximized the tension of the weave, so that after washing, the denim actually becomes even more stiff and the weave even tighter
7. Sugarcane : Sugar Cane ’ denim by traditional Japanese dyeing techniques by hand and not by machine. The first model ‘ Sugar Cane Awa ’ is made of sugar cane denim dyed by Awa indigo. Sugar Cane were the first in the world to produce a selvage-denim fabric made from woven cotton yarns and sugar cane fibers. otton and sugar cane yarns are dyed completely by hand with 100% natural indigo.
   

Italian Denim Brands

1. Diesel : The world famous jeans brand. Needs no introduction ! . Links : a) Financials b) Buy Diesel Jeans
2. Armani Jeans :Armani Jeans is a bridge-line collection of denim-related clothing created in 1981 by Giorgio Armani. Unlike Armani’s lower-end collection Armani Exchange, Armani Jeans is mainly sold in department stores instead of freestanding stores.
3. Miss Sixty :

Swedish Denim Brands

1. Acne : A ton of variety in mens’ fits, and repeat winner of ‘Designer of the Year’ by Swedish Elle.
2. Cheap Monday : Founded in 2000 by Örjan Andersson, originally as a second hand clothing store, in a suburb of Stockholm. The name of the brand originates from the fact that the original store was only open on Sunday.Being cheaper than other brands, and with tons of crazy prints and colored washes, it is liked by high school students a lot. Link.
3. Nudie : Men’s Jeans made from the best Italian, Turkish, American, and Japanese qualities using the best techniques. How they are made?
   

Netherland (Dutch) Denim Brands

1. G-Star : G-Star offers a well-balanced range of jeans in various designs, the right range of fittings and attractive washings. Products made for denim connoisseurs by denim connoisseurs.
   

US Denim Brands (L.A denim brands included)

1. AG Adriano Goldschmied : Starting out as a small boutique line in 2000, AG is a brand that is centered on recreating vintage denim washes.AG continues to evolve its “AG-ed Vintage” collection by introducing new fits, washes and fabrications. For Spring 2010, the brand will launch a Khaki Program, where the “AG-ed” 3-D whiskering technique is applied. Links : a)Some details
2. Paige Premium Denim : Paige Premium Denim, LLC was founded in 2004 by fit model Paige Adams-Geller on the principle that you don’t have to be a size zero to look great and feel great in a pair of designer jeans. She was the body behind the brands like 7 For All Mankind, Lucky Brand, Citizens of Humanity, Guess and used her expertise and unique values to create the “perfect fitting jean.”
3. 7 for all Mankind : Owned by VF Corp. since 2007 ,7 For All Mankind was the first company to truly bring premium denim to scale in 2000.7 For All Mankind’s premium jeans literally exploded onto the scene, quickly earning critical acclaim and an immediate following for its innovative use of fits, fabrics, and finishes in denim.Hollywood celebrities like Angelina Jolie, Cameron Diaz, Jennifer Garner, Liv Tryler and Ben Affleck endorsed the ‘Sevens’. Links :a)VF acquires 7
4. Siwy Denim : Launched in Spring 2005 in downtown New York City, Siwy offers the ultimate denim collection: vintage-inspired, sexy, fashion-forward designs with perfected finish, detail, and fit. Each piece is finished with hand-crafted labels made out of vintage feedsack cloth.
5. Earnest Sewn : Earnest Sewn brings forth two concepts: 1) process innovation and 2) heritage. Everything from "Twice Sewn" [stitching] process, to specialized hand-sanding techniques, which are worked on by one expert artisan per pair, to coffee-stained hang tags and individually wrapped craft paper set it apart from other labels.
6. Current/Elliot : Born as late as 2008 when Emily Current and Meritt Elliott, both stylists, met with friend Serge Azria, CurrentElliot seems to have gained fame rather fast. They are reputed to have started the BoyFriend Denim trend which is been adorned by Hollywood celebrities like Katie Holmes , Victoria Beckham etc.
7. J Brand : J Brand was co-founded by denim manufacturer Jeff Rudes and former stylist Susie Crippen.The two set out to create classic and sophisticated jeans with the emphasis on fit.J Brand – women’s- launched as an exclusive at Ron Herman’s Melrose jeans bar in the spring of 2005.The brand had immediate success, and J Brand’s introduction of their skinny straight leg made them the first American-made premium jeans to drive this trend. The also have a maternity line — Mama J by J Brand.In fall 2008, J Brand introduced a Men’s line under the label, J Brand Denim Co.

DENIM MANUFACTURING PROCESS

Yarn Manufacturing

Open End Spinning

Ring 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.

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.

Indigo Dye Range

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.

Warp Preparation

In the warping process, individual strands of yarn are removed from yarn packages prior to being gathered into a rope form suitable for dyeing. Individual strands of warp yarn (the length-wise yarn in a fabric) are gathered into rope form and wound onto a log, thus forming a ball warp.

Two rope-dye ranges enable ACG to produce pure indigo, sulfur bottom, sulfur top, and colored denim yarn. The yarn goes through scour/sulfur dye, wash boxes, indigo dye vats, over a skying device (to allow oxidation to occur), through additional wash boxes, over drying cans and then is coiled into tubs which are transferred to the Long Chain Beaming process.

Long Chain Beaming separates the dyed yarn into individual strands, parallels the strands, and winds them onto a large section beam in preparation for Slashing. The Slashing process takes section beams, coats the yarn with a starch/wax solution, and winds the yarn onto a loom beam.

Omni Plus Looms

A starch/wax solution is applied to enable the yarn to withstand the abrasion and tension it will be exposed to in Weaving. The solution also reduces the fuzziness of the yarn, thus eliminating a pilling effect in Weaving.

Weaving

The weaving process interlaces the warp (length-wise indigo dyed yarn) and the filling (natural-colored cross-wise yarn) producing 100 percent cotton denim in a variety of weights and styles.

The Finishing Range

The Finishing Range brushes and singes the cloth prior to the cloth entering a finishing solution. The cloth is then pulled to the proper width, skewed, dried and rolled for the next process.

The Compressive Shrinkage process reduces the amount of shrinkage in the warp or lengthwise direction that a finished garment will have after laundering. As the cloth enters the machine, it is moistened with water and then fed between a thick rubber belt and a heated steel cylinder where approximately 14 percent shrinkage in the warp yarn takes place. After drying, the cloth is rolled onto an "A" frame.

The EVS uses cameras to inspect denim for defects.

Every yard of cloth must pass rigid inspection standards. An inspection process utilizes an I-Tex 200 model Elbit Vision System (EVS), an automatic fabric inspection system, that evaluates the quality of the denim by identifying visible defects that result during spinning, weaving, dyeing and finishing at Littlefield. This system can detect defects as small as 0.5 mm on fabric up to 68 inches wide at speeds up to 42 yards per minute. As denim is fed through the system, three cameras photograph the back of the fabric, and four cameras photograph the front. These cameras continually photograph the fabric and save only the frames containing identified defects. They also log all pertinent information such as lot number and the exact location of the defect on the fabric. This information then is fed to the cutting tables where computers help locate the defect. This high-tech system increases fabric inspection efficiency and reduces garment seconds. At the 3/1 process, the cloth is measured and cut into rolls of proper quality and size. Each roll is carefully weighed to ensure correct weight and yardage per roll.

INDIGO

Indigo is the primary color of blue jeans , it is an important dyestuff with unique shade of blue color.The dye gives a brilliant and eye catching blue color to the fabric. Indigo has a low affinity for cotton ,therefore deep blue dyeings are only possible when and oxidation is done several times.The color partially penetrates the yarn , and imparts the surface blue color.The dye then fades gradually fades from the surface of the fabric naturally.


Natural Indigo


Indigo dye is an important dyestuff with a distinctive blue color. The natural dye comes from several species of plants.A variety of plants have provided indigo throughout history, but most natural indigo is obtained from plants in the genus Indigofera, which are native to the tropics. In temperate climates indigo can be obtained from woad (Isatis tinctoria) and dyer's knotweed (Polygonum tinctorum), although the Indigofera species yield more dye. The primary commercial indigo species in Asia was true indigo (Indigofera tinctoria, also known as Indigofera sumatrana). In Central and South America the two species Indigofera suffructicosa and Indigofera arrecta (Natal indigo) were the most important.

Properties of Indigo

Indigo is an insoluble dye ,a dark blue crystalline powder, which has to be reduced with suitable reducing agents to make it soluble in water,Indigo works by a chemical reaction called oxidation reduction.Indigo does not dissolve in water. It must be reduced — i.e. the oxygen must be removed— in the presence of alkali by a reducing agent such as thiourea dioxide (thiox), sodium hydrosulfite, Zinc, or bacteria. Upon reduction, indigo becomes colorless and water soluble. In this state, indigo has a high affinity for cellulosic fibers and enters the open spaces of the fiber. The dyed fibers are then exposed to air, which oxidizes the dye molecule back to its insoluble form. The insoluble dye particles are trapped inside the fiber, coloring them permanently blue. Unlike most dyes, indigo forms a mechanical, not chemical, bond.


A.Indigo is a dark blue crystalline powder that melts at 390°–392°C.

B.It is insoluble in water, alcohol, or ether but soluble in chloroform, nitrobenzene, or concentrated sulfuric acid.

C.The chemical structure of indigo corresponds to the formula C16H10N2O2.

Click for Complete Chemistry of Indigo


D.The naturally occurring substance is indican, which is colorless and soluble in water. Indican can easily be hydrolyzed to glucose and indoxyl.

E.Mild oxidation, such as exposure to air, converts indoxyl to indigo.

F.Indigo is a frequency range of visible light, from 440 to 420 nanometers in wavelength, placing it between blue and violet.

Indigo dye

Indigo has despite many other blue dyestuffs kept his popularity. This by no doubt is achieved by the fact that Indigo has a number of properties which have in this combination not yet been achieved by other single dyestuffs.

The main properties are:


• Pleasant colour shade.


• Possibility to achieve by simple repeated dipping, deep marine blue shade.


• Possibility to dye cotton in cold dye bath.


• Competitive in price.


• Possibility to achieve an acceptable colour fastness and the exceptional advantage by repeated washing of fading colour, to keep the colour shade that always a clear, pleasant blue shade result.


Indigo Application

Three basic steps for indigo application are .



1.Dissolving the dye by reduction involving vatting and loosening up.



2.Dyeing from the vat.



3.Oxidising in the air.



Since indigo has a low affinity for cotton, deep blue dyeings are only obtained when dyeing and oxidising are repeated several times.

Dyeing Methods

Five major Indigo dyeing methods for the basic denim are

1- Indigo rope dyeing process


2- Indigo one sheet dye slashing



3- Indigo double sheet dyeing



4- Loop dye 1 for 6 (continuous dye slashing)



5- Loop dye 1for 6 with dyemer (continuous mercerization dyeing and sizing).

WHISKERING INCONSISTENCY ON JEANS - A SOLUTION

Whiskering inconsistency is a regular problem in denim jeans production . It requires highly skilled workers to create the right kind of whiskers consistently.

However, even with the highest levels of consistency, the element of uncertainty remains and whiskers may not be uniform across the entire production .

Modul SRL of Italy has devised moulds for jeans which it claims can provide a very high level of consistency by providing inbuilt whiskers on its moulds. This enables the worker to just scrape normally on the jeans and the whiskers appear uniformly without the effort on the part of the worker to create the same and the whole whiskering and hand sanding process is complete within 4 minutes.The company claims to be the only producer in the world of a technology to replicate the vintage look that they sell to contractors around the world and big denim producers .

How do these whisker moulds work ?

Take a look at this video first to understand how this mould system works
As you can see from the video above, the worker scrapes normally on the jeans put on the Modus Moulds and whiskering appears itself in a predetermined pattern. Thus the whiskering can be done by a relatively inexperienced worker also.

These moulds look quite interesting if they perform consistently. However, the cost of these moulds may be an issue as they are not cheap .

How Can A Jeans Factory Use These Moulds

• A factory needs to buy at least 5 moulds to start using this system and since each mould costs around Euro 700, an investment of about 3,500 Euros is required to make a beginning.

• All moulds are expandable to three sizes – small ,medium and large.

• Each mould lasts 5000-7000 inflations – though it depends on the skill of the operator.

• Each mould can produce only one whisker pattern. If the client needs to recreate any whisker pattern (from any jeans eg) , Modus can recreate the mould for the same and ship to the client within 1-2 weeks.

The company also provides protos moulds prized at Euro 370 which can be used for sampling purposes.

Here are some whiskers patterns created using these moulds