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

DENIM DRY PROCESSING

The distressed jeans that we see around everywhere undergo a wide variety of wet as well as dry treatments to get the desired effects. Here I shall try to explain some basic Denim Dry Processing techniques. In the creation of vintage denim jeans, dry processes play a very important role and hence important to understand.

Denim Dry Processing - Basic know how

Destroying denims is as much an art as it is a technique. Details are added using a fine abrasive paper on a scraping tool. And extra whiskering can be added with sand paper. Sometimes a bit of local tint staining is being done into the local areas to emphasize the lighter parts.

The jeans then go for a washing with pumice stone to blend in the whiskering and tinting / over dyeing. Where the folds and wrinkles go is where the art part comes in, it’s often through observation of where wear patterns are typically found. For some of mine I have several pairs of old well worn thrift store jeans that I use as a template to guide where I want the wear patterns. I chalk in where I want the details and then they are finished off site by me in my finish workshop. Some of what is done to customize jeans are patented secrets, no one other than those who work for these companies knows the exact techniques or the abrasives and chemicals used to achieve certain special effects.

Below is list of operations being carried out on denim garment to achieve VINTAGE (used/worn out) look……

• Hand Sand / Hand Scraping
• Sand blasting
• Whiskers
• Chevrons
• Knee Star / knee whiskers
• Hot Spot
• Tacking
• Grinding
• Damages / Destruction
• PP Spray
• PP Brush / towel
• Patch / repair
• Bleach spots
• Resin application
• Pigments & Local tint application etc….

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1.Denim Hand Sand / Scraping

Hand sand is step which is generally being done in rigid form of garments to get distress look. Locations can be front thigh & back seat or its can be overall / global application as per Standard. Emery paper is being used to scrape the garments in particular placement & design. Emery paper comes in different number generally start from 40 till 600 and above , higher the number finer the emery paper, lower the coarseness of the paper. In garment industry from 220 , 320 & 400 number papers are most popular & widely used.

Purpose of doing this process is make used worn out look to the garments.

The most important factor is to select right number of paper according to the fabric strength & intensity need. Feathering / merging white sanded part to dark blue area in such way that it should look natural & not artificial.

Scraping can be done on inflated rubber balloons for better effect ( horizontal or vertical its up to operators convenience ) , even it can done plain wooden board of garment size & hand pressure should be uniform in order to get better results.

Hand sanding must be started from intense part & feathering out on less intense part gradually. One garment must by done by one operator only to have balance intensity on both the legs.

2.Sand Blasting

This process is isolated now a days due to health hazards & buyers do not like the results of sandblast because its covers the characteristics of fabric. This process being done by using different kin d of sand blown to garments with air pressure to rub out the color.

3.Whiskers/ Moustaches , Chevron , Knee Star, Hot Spot

On Denim, whiskers / Mustaches , Chevrons are nothing but the worn out lines / impression generated by natural wearing on hip & thigh area. There are many designs & pattern available.

This is being done manually with help of sharp edge Emery paper rolled on fine wood stick or pasted on plastic material. Before starting execution placements & pattern must be marked on garments, this will help operator to execute the pattern right to match the aesthetics of garment.

Hot spots are heavy/intense area on thigh or knee which is made purposely to create used look & on knee area if any whiskers line are there, called knee star.

All above operations are carried out in width direction hence its appears intense than hand sand with less strokes, because hand sand is carried out in length direction.

4.Tacking & Grinding

Tacking: is a process which is being done by swift tag machine with the help of plastic or nylon tag pins in rigid form of garment to get very heavy contrast ( rigid & washed ) on waistband, bottom hems, back pocket & front pocket corners etc.. after completing wash cycle, it must be removed from garment before making softening.

Grinding: is being done on pocket edges & bottom hems edges by running against abrasion surface or stone to achieve worn out effect. Many different make of machines & pen grinding tools are available in the market which runs with pneumatic system.

5.Damages/Destruction

One of the most popular distressing effects currently , ‘Destruction’ is an art which make denim look unique & used. To make destruction pen type of stone tools being used in mid of wash process to apply on desired area. It can also be achieved by cutting it thru knife the warp yarns & keep the weft yarn as is to show white thread. Holes also can be made by cutting weft & warp yarns. These are all manual processes & every garment will look unique & different than others.

6.POTASSIUM PERMANGNATE SPRAY/RUB & BLEACH SPRAY

PP Spray is being done on denim garments to achieve local abraded area to appear whiter than back ground indigo color shade. This can be applied by spray gun or by towel dipped in to PP Solution & rubbed on desired area followed by neutralization in wet process. This process can be done in rigid after doing hand scrape or in the middle of the wash. Doing after enzyme or bleach cycle will give more natural & white effect that doing in rigid. There are many additives can be added in order to achieve desired intensity and look.

The same way bleach solution also can be spray or rubbed on the garments on desired area. But this process is very complicated & needs highly skilled operators to execute it followed by immediate neutralization.

There are many parameters needs to be taken into control for doing PP or Bleach spray…. Spray gun pressure, width of spray, flow & way of spraying.

Note:Safety of operators must be taken in to consideration and it must be ensured that he should wear mask, gloves & eye glasses etc…

7.Patch & Repairs along with Bleach Spots

These are totally manual processes to give uniqueness to Denim and to make it look VINTAGE. First cut or damage the units intestinally to desired area & then make hand repairs or machine repair to look natural. Diluted bleach can be used to spot the desired area followed by neutralization in wet process.
These process are time consuming hence productivity is low & reproducibility is very difficult but similar aesthetics can be achieved.

When we talk about Vintage denim, every garment should look unique & not a photocopy !. These garments are sold at very high prices so customer should have a feeling of uniqueness & feeling different from others. Vintage denim are signature/ autograph of a brand & its image.

8.Resin Application( 3D Effect )














Resin ( Formaldehyde free ) being used for achieving 3D effect ( 3 Dimensional ), Rigid Look etc. This process can be done by spraying or dipping the garments in to Resin, Catalyst, Silicone & PU solution in right combination according to the fabric strength & desired effect needed. After application of resin solution in right proportion, make manual designing as needed on the thigh, hip & back knee area to get 3Dimentional effect. After making it , it should be manually dried with hot press or hair dryer & then must be cured in oven at right temperature, time as mentioned in resin product manual.

If resin not cured properly , 3 D effect will not be permanent & can cause skin irritation/rashes to the wearer. Highly skilled operators needs to execute this process in order to get consistency & uniformity.
Whole garment can have crushed look by resin dip & crushed manually followed by oven curing. Silicone plays an important role in getting softer hand after oven.

Special streaky effect & Crackles also being done by applying resin on desired area followed by scraping & pp spray then neutralization.

9.Pigments & Local Tint ( Staining) Application

Need to choose right color of pigment or tint with binder or fixer to apply locally on denim to get vintage look. This process also needs an artist to execute it nicely to merge the tint with ground indigo color & should not look too artificial. Pigments & Local tint also can be applied through spray gun or rubbing on desired area of denim garment. After application its must be cured in order to have permanent effect on jean.
As we can see from all the dry denim processes mentioned above, they are mainly manual processes. The quality of the worker can make or break the garment. Hence , great care has to be given to select the right personnel for these jobs.

ACID WASHES ON DENIM JEANS

 

Acid wash is again becoming popular on denim jeans and we are going to see more of acid washes in the coming seasons. Here , lets have a quick look at the acid washing process .
An acid wash finish treatment creates significant contrasts in the color of the denim material. It can be done on Indigo & Sulphur base fabric garments. As the randomly faded, acid washed style came into vogue in 1980s, the process of treating denim in such a way began to become increasingly refined. Some tried to use a method similar to the stonewashing, yet the fading did not occur as dramatically or throughout the material.

In 1980’s this washed being launched as first innovative finish on denim ever. This was being done by soaking stones in Bleach and making acid wash effect followed by neutralization. But this process was not so re find to get some how consistent & smooth effect on denim. In early 2000 some laundry tried doing the same wash soaking thermocol bolls in bleach or pp solution to get this desired effect. While this process can be done using either light bleach, chlorine , potassium permanganate etc.

The most popular is PP Bleach and will produce the best acid washed results. Doing the process is very simple , but following all parameters in correct way to have right & repeatable results. The load size of garments, machine drum diameter, quantity of soaked stone / towels & skilled operator. Initially, the Acid Wash process involved soaking pumice in Industrial Strength Chlorine .

However, it was discovered that potassium permanganate was more controllable and just as strong an oxidizer. They simply marinated pumice stone in it and then vacuum packed the stone to the required moisture level. Acid wash was a chemical process on denim that stripped the top layer of color off to a white surface with the undertones of navy blue remaining in the jeans.

The Materials

The process of acid washing jeans involves porous pumice stones or small towel pieces and chlorine or Pp Bleach, such as you would put into a bucket or in drum for soaking process. Sodium-bisulfate is used in the second washing for Neutralization. Also recommended is access to two separate washing machines. One for Acid Washing & another one for further process i.e. Neutralization etc.

The Acid Washing Process On Denim Jeans

The process of acid washing jeans used chemicals, stripping off the color of the top layer, leaving the white fabric exposed. The color remained in the lower layers of the material, giving it a faded look. Acid washing could be done overall or made to look splotchy.

1.Soak porous pumice rocks or pieces of towels in chlorine or PP bleach solution for about 20 minutes to an hour. The longer you soak the pumice or towel, the more prominent the effects will be.

2.Once the stones are saturated with chlorine/pp, remove excess water from stones/towel then put the stones in machine followed by the jeans in a washing machine for about 20 minutes. Make sure machine do not have single drop of water, open the drain during complete process

3.At this time, check on the jeans to ensure they look acceptable, and then move them to another washing machine for a regular washing process. Too long in the first machine can totally bleach or ruin the jeans, and too little time may not produce the desired results or can make patchy appearance. Check on the jeans once every 10 minutes or so during the second wash process of neutralisation to ensure the desired look is achieved.

4.Next, fully dry the jeans in a dryer that gets nice and hot.

Precautions

Any time we mess with chemicals such as bleach or chlorine or PP, be sure to protect workers by wearing mask & aprons , so it is best to be fully prepared. Also, protective rubber gloves and safety glasses are highly recommended. These products can burn skin and eyes pretty badly. About Author : 3E’s Consultants, Group of experts, focused on Denim Fashion, Providing consultancy to all Denim Garments Finishers

INDIGO-DYEING

INDIGO- DYEING VARIOUS METHODS

EXPLAINED AND COMPARED

The indigo dyeing and processing methods -currently used – for dyeing indigo warps were introduced from 1978- 1987 to obtain a higher productivity and savings in dyeing or to achieve the required darker shades (hard rock washing, super blue, soft denim), or softness of the yarn for final finishing. The following table gives you a comparison of the possible processing stages such as:

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 1 for 6 with dyemer (continuous mercerization dyeing and sizing).

For the five major Indigo dyeing methods for the basic denim, super blue denim, soft denim, stone wash denim, we also must take into consideration that a certain appearance of the garments is only achieved after a certain washing method. (Chemical washing, stone washing, hard rock washing), use of certain sizing agents (soft denim) or irregular appearance in warp or weft direction by using a yarn with slubs and neps (antic denim).

The final finishing methods have influence on fabric construction and dyeing methods.

CHEMICAL WASHED DENIM

The creator of snow wash denim or of f-side denim is Edwin Co. Limited Japan. These chemical washed types of ready made garments show less tensile strength and a harder hand.

STONE WASHING

With soft stones it takes 20 – 30 min. to achieve the desire surface appearance.

DRY BLEACH

Soft rock are socked with chloride and the garment treated in washing machines.

HARD STONE WASHING

Treatment takes approx. 3 – 4 hours. A very soft hand the garments is achieved. Due to the extended time of treatment in washing with hard rocks the strength of fabric is influenced. This treatment requires improved yarn quality and deeper dyed shades. Hard stone washing fades out partly at hems and stitched lines.

SUPER BLUE

Deepness shade is achieved by dyeing in 8 – 12 dye boxes with rope dyeing methods. With mercerized yarn where the colour stays at the surface of the yarn (ring dyeing) with continuous loop dye range with integrated mercerizing and dyeing unit (dyemer).

BLACK DENIM

Sulfur dyed, padazoic dyed etc. on continuous dyeing sizing machines or loop dye ranges.

INDIGO DYESTUFF AND ITS CHARATERISTICS

Indigo has despite many other blue dyestuffs kept its 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:

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  Pleasant colour shade.
  
  
  
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  Possibility to achieve by simple repeated dipping, deep marine blue shade.
  
  
  
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  Possibility to dye cotton in cold dye bath.
  
  
  
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  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. The following drawing shows the symbolic built-up of dye stuff of the yarn according to the multi-deep process.

The sketch shows how Indigo layers one after the other are placed on the surface of the yarn then again scraped off, similar to knife through force or tension or by washing. An Indigo has only a very low affinity and the depth of colour of the fibre is achieved by repeated dipping / oxidation. Each dipping cycle occur in a certain balanced manner as dye stuff is observed by the fibre at the same time and part of the already

oxidized dye stuff is reduced and migrates from the fibres.

With increasing dipping operations , the balance of absorption / migration moves towards migration.

A very important factor for the reduction of migration is the squeezing effect and the oxidation which follows. A high squeezing effect promotes a quick and thorough oxidation and reduces the migration and reduction in the following bye bath.

With the low squeezing effect ie with high liquid absorption, the purely visual impression of a good oxidation can be deceptive as the outer colour skin looks blue. In the core of the thread however less vat dye stuff may be deposited Let us have a close look at the different dyeing systems.

CONVENTIONAL CLASSICAL

CONTINUOUS INDIGO ROPE DYEING

The classical rope dyeing system is very labor intensive and consists of:

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  Ball warping
  
  
  
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  Indigo dyeing
  
  
  
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  Rebeaming on long- chain-beamer
  
  
  
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  Sizing
  
  
  

Yarn from the ring spinning machine is wound on automatic winding machines on to a suitable package either cylindrical or 5057 cone. The winders are directly linked to the ring spinning frames and the cops joint by splicing. OE yarns are directly creeled up on the Ball warper.

The required No. of ends (usually 380 – 420 ends) are assembled into a rope. These ends are wound onto a core. The rope is guided similar as a cross wound package and wound into a ball, length of ball approx. 12 – 15.000 meters.

A lease is inserted at the start and end of the rope. The facilitate Rebeaming every 1000 meters an additional lease is inserted. Usually 18 – 24 ropes are simultaneously process on the rope dyeing machine. Prior to dyeing, the ropes are boiled out and treated with caustic-soda and wetting agent to remove from the cotton oil, impurities which could influence the fastness for the dye.

To dye with indigo, the ropes are immersed into the dye-bath. To dye in rope 30 – 60 seconds immersion (20 meters yarn) and 60 - 180 seconds are required for the oxidation of the Indigo dyestuff to ensure that also ends in the centre of the rope are equally dyed. Please note that squeezing pressure is important- 5 tons- as fastness of colour and shade depends on even squeezing pressure. The comparatively long immersion and oxidation time requires a comparatively expensive equipment of machinery.

In order to obtain the required deep shade of blue colour the ropes are immersed 5 – 6 times in a sequence of dye boxes with an oxidation range - so called skying - after each dye box. (Indigo belongs to the group of the vat dyes which is water-soluble in reduced solution and becomes an insoluble pigment when oxidized.

Having passed the dyeing and oxidation rage the ropes are guided through 2 or 3 washing boxes to wash off excessive dye .In the last box softener are added to ease the opening of the ropes. They are dried in a series of cans. The dried ropes which contain 380 – 420 ends are then deposited into large coilers .Rebeaming with 300 – 380 ends per rope is easier. These coilers are placed behind the long chain beamer where the Rebeaming and opening of the ropes takes place. In order to guarantee even yarn tension through Rebeaming on to a back beam ready for sizing the ropes are guided over a tension device which is placed approx. 10 -11 meters distance from the long chain beamer. Broken ends which very really happen during process of the rope dyeing are repaired at this process stage. Initially these machines were supplied without yarn stop motion but are available now a days on special request. This is of major importance as lost ends, fluff, 3 – tail ends and yarn remnants can cause inferior performance in weaving.

The so prepared beck beams are now sized in a sizing machine preferably with 2 size boxes. The size pick up varies between 8 – 10%. In Europe mainly modified starches with binders are used, whilst in USA certain low % of PVA is applied in combination with starches by some companies. Depending on the final finishing process (washed denim) with no filler also CMC gives excellent performance in weaving. Special size mixes for soft denim will be discussed separately. We recommend however not to use PVA for sizing of denim as a surface of denim may show a leather skinned appearance.

CONTINUOUS SLASHER DYEING SYSTEM

Contrary to the Indigo rope dyeing system, for the continuous slasher dyeing and sizing back beams are used. That means that the total No of ends required for a weavers beam are dyed, dried, sized and dried simultaneously. The back beam contains similar to rope 380 – 420 ends but distributed evenly over the width of 140 or 160 cm between the flanges so the end lay parallel to each other, warp length 12 – 15.000 meters, similar to the rope dyeing system the full No of ends are pretreated (washed) dyed in 4 dye boxes and oxidized, no softener are used in the last wash box.

CONTINUOUS INDIGO DYEING AND SIZING PROCESS

We must however consider that the squeezing effect is lower and therefore the danger of streakiness and shade variation from centre to out side is also higher. Consequently it would be better to reduce the warping width rather to 140 cm instead of using warper beams with 160 – 180 cm warping width.

The immersion time in the dye boxes is approx. 10 – 15 seconds and time for oxidation 30 – 60 second. The final result is a weaver’s beam. This system allows the installation of less expensive dye rage and less additional preparatory machinery.

One of the disadvantages previously when warp preparation (knots, weak, thick places) was not kept at a very high level was that ends sown in the dyeing range could cause major color variation through machine stops.

DOUBLE SHEET CONTINUOUS DYEING

Patents applied for double shade dyeing by E. Godau date back as 1976. With the system dyeing sizing is done in 2 operations. The main reason for dyeing of 2 sheet simultaneously is achieved a more even dyed sheet, that means 8000 – 8200 end are dyed, oxidized, dried and the full length of the warper beam 12.000 – 15.000 meters flange diameter. These beams are transported with the aid of air cushions to the sizing machine and the yarn sheet sized in double size boxes. Immersion time and oxidation time is the same as with continuous slasher dyeing. Indigo full-width warping process


With double sheet dyeing the linear warp thread density is doubled. Therefore: Squeezing effect is increased,
An even squeezing over the whole width is achieved, Condensation and concentration of ends at one spot show compared to single sheet dyeing no colour strips formation, streakiness or shading in the finished fabric. The production out put of the dyeing is increased by 75%. Dyeing of 3 layers of yarn simultaneously is possible but very difficult to control the beaming on 3 big warp batches.

Unfortunately the double sheet dyeing machine as well as the rope dyeing range cannot be linked with a sizing machine which must be regarded as disadvantage as the processes of dyeing and sizing must be carried out separately.
Loop dye system 1 for 6

Similar to the sheet dyeing systems 10 – 16 warper beams with the total number of ends required for the weaver beams are used. The warper beams are placed in a moveable warp creel which can be loaded whilst one set is in potation.


The yarn sheet is guided to the soaking bath through a feed-in system with tension compensation rollers. The soaking bath has the task to prepare the yarn for the following dyeing operation.

The yarn sheet after having been immersed into a single indigo dye bath runs into a long loop where oxidation takes place. As you can see from the slide the back beams are inside the yarn sheet passes through the dye box as often as necessary to obtain the required deepness of shade. One of the advantages is:

Ideal, utilization of Hydrosulphite through squeezing 4 – 6 layers simultaneously and oxidation of yarn in a comparatively long oxidation loop. After the oxidation the yarn sheet is guided through 2 washing boxes into a yarn accumulator and finally on to a series of drying cans, dried up to 25 – 30% final moisture content prior being immersed into size boxes, dried and wound onto a weavers beam.


The molecules are controlled DC drive to maintain warp tensions. Temperatures are automatically controlled as well as the PH value in the dye box. The automatic control unit of the PH value supplies automatically hydrosulfite and caustic soda to stabilize the present value from the start to end of a dye set.

All rollers arein contact with the dyed sheet are fluted, they keep the sheet in position and reduce deposit of dye and build-up of other deposit (fluff). In addition to width is controlled by guides to ensure even distribution of the yarn layer over the whole width of the dyed sheet. All accumulators placed between washing boxes and drying cans guarantees a continuous production of the dye range when a weaver beam has to be exchanged at the head stock. The creels can be loaded with back beam with 1200 mm diameter which allows to warp approx. 36.800 meters of yarn, count No 7, 5 (tex 78) or 50.000 m count No 10 (tex 60). This means that depending on the count normally one cyl-spool is used in warping to fill a warper beam.

WARPING SPEED

PRODUCTION

Speed varies between 1000 m/min, 35 m/min. No 5, 5 (tex 107) and 42 m/min. No 10 (tex 60)

MACHINE STOPS DURING SIZING

For 36800 m, 4 recorded on expansion comb.

WASTE OF MATERIAL

Approx. 15-20 kg per set.

TIME REQUIRED FOR CHANGE OF SET

2 hour

LINEAR WARP DENSITIES IN THE SQUEEZE

The linear density in the nip is calculated in the same manner as for sizing.

Q= linear thread density

F= ends in cm -1

D= diameter of yarn

D= 0,921 mm = 0,921 = 0, 29125

Nm 10 = 3.1622

Q= F x D

As already mentioned previously the warp density has an influence on colour fastness. A higher squeezing effect is achieved due to the over laying of the watp ends this also gives more side to side squeezing, therefore reduce strips formation. The high squeezing effect results also in better, quicker and proper oxidation and better colour fastness.

It must be mentioned that recommended dip and oxidation times on warp dyeing ranges are of little use if not the squeezing effect is taken into consideration. Under a given squeeze pressure, for instance 500 kg the squeezing effect of the mentioned 4- dyeing systems can be compared. We can see that similar squeezing effect can be achieved with the loop dyeing system 1 for 6 (75%) as with rope dyeing 70 – 110%. Double dyeing with 2 layers width with 150 cm gives approx. 80% squeezing effect, whilst single sheet slasher dyeing varies depending on count between 100 – 130%.

Loop dye 1 for 6 Rope-dyeing Slasher-dyeing
 
As only one short indigo dye bath is deeded only one feeding tanks, no separate feeding of chemicals is necessary.

Dye liquor is use in 1500 1 instead of 6-4500 1, therefore less chemicals are in use at same time. Lowe power consumption.

Fine counts can be dyed as well (No 30) For dark shades, black shades or other shades needed by fashion, other indanthrene dye stuff can be directly added into the indigo dye bath (indanthrene yellow or orange).

LOOP DYE 1 FOR 6 COMBINED WITH DYEMER

The demand for dark shades specially dark marine blue for super blue denims also led to new ideas in indigo dyeing ranges have been increased between 8-15 dye boxes with corresponding oxidation ranges.
In some cases Hydroxyaceton has been specially treated with high frequency. Besides achieving a darker shaded with the desire greenish touch it is very suitable for biological treatment. In order to achieve ring dyeing, mercerized yarn has also been used. Mercerizing prevents penetration of dye stuff into the inner code it is suitable for this purpose to obtain an optical blue effect and superior colour fastness and behavior in washing. Mercerizing is very costly, therefore new ways in continuous mercerizing and indigo dyeing was found.

DYEMER

The dyemer range is integrated.

For impregnation padder for hot caustic solution is placed after the heating system. The yarn is guided over cold cylinders and with an adjustable roller the tension of the yarn sheet can be adjusted according to the required tension prior to the scouring in 2 more boxes. After having passed this, the yarn sheet is immersed into the dye box and the same process as with the loop dye method is repeated.

CONTINUOUS DYEING AND SIZING ON THE DYEMER RANGE


If fashion needs other colours than indigo blue it is comparatively simply to dye and size on this range.