INDUS INSTITUTE OF HIGHER EDUCATION
KARACHI
THE STUDY OF DENIM WASHING
A PROJECT SUBMITTED TO
THE FACULITY OF TEXTILE SCIENCES
IN PARTIAL FULFILMENT OF REQUIRMENTS FOR
DEGREE OF
BACHELOR OF TEXTILE SCIENCE
(B S TEXTILE)
SUPERVISED BY:
ENGR ABDUL SALAM
FACULTY MEMBER.
Email: [email protected]
SUBMITTED BY:
SYED ASIM NAJAM
UMAIR MAJEED KHAN
ACKNOWLEDGMENTS
All thanks are due to Almighty “ALLAH” the most beneficial and merciful who enabled us to complete this project.
The completion of this project is perceived as the fruitful result of and incredible effort, devotion and hard work. It can be stated without any hesitation that this thesis is the outcome of the joint effort of all concerned by successfully negotiating the various tedious problems and hurdles.
We are particularly thankful of Sir Adbul Salam our project advisor for the guidance and valuable cooperation render by him at any stage regarding this project. He fully indulged himself to facilitate our job whenever approached him to seek guidance regarding this study.
Special thanks are reserved for the Head of Textile Science Department Sir Hasib-u-Salam for encouraging and motivating throughout the successful completion of this project. We are very thankful to each and every person of Ragby Industries specially Sir Ejaz Shah, who make ourselves very comfortable during our whole internship program, who led us to complete this project work.
Faculty of Textile Science
INDUS INSTITUTE OF HIGHER EDUCATION
Karachi.
Certificate
I am pleased to certify that the following students have
satisfactorily carried out a thesis work, under my supervision on
the topic of “Denim Washing”
I further certify that his thesis is worthy of presentation to the
Faculty of Textile Sciences,
INDUS INSTITUTE OF HIGHER
EDUCATION
Karachi
for the degree of Bachelor of Science in Textile.
1. Syed Asim Najam
2. Umair Majeed Khan
HOD Textile Science:
__________________
External Examiner:
__________________
TABLE OF CONTENT
Content Page No.
Chapter 1 1.1 Introduction 7 1.2 Back ground 7 1.3 History of denim 7 1.3Literature Review 9 1.4 Area of study 10 1.5 Expected Results Chapter 2 Warping 2.1 Introduction 11 2.2 Ball warping 11 2.3 Beam warping 12 2.4 Components of machine 12 2.5 Procedure of warping 13 Chapter 3 Dyeing 3.1 Introduction 14 3.2 Classification of dyes 14 3.2.1 Direct dyes 14 3.2.2 Reactive Dyes 15 3.2.3 Sulphur Dyes 15 3.2.4 Vat dyes 16 3.3 Denim dyeing 18 3.3.1 Rope dyeing 20 3.3.2 Slasher dyeing 21
3.4 Difference between rope dyeing and slasher dyeing 24
3.6 After-washing process and drying 27 3.7 Sizing 27 3.8 Drying zone 28 3.9 Accumulator 28 3.10Leasing zone 28 3.11 Expansion comb 29 3.12 Beaming 29 3.13 Transportation of beams 29 Chapter 4 Weaving 4.1 Introduction 30 4.2 Basic weave design 30 4.3 Weaving of denim fabric 31 4.4 Typical denim construction 32 4.5 Non-conventional denim fabric 33 4.6 Shedding system 34 4.6.1 Crank shedding 34 4.6.2 Cam shedding 34 4.6.3 Dobby shedding 35 4.6.4 Jacquard shedding 35 4.7 Classification of weaving machine 36 4.7.1 Shuttle weaving 36 4.7.2 Shuttle less weaving 37
Chapter 5 Faults in production of denim
5.1 Faults of warping 41 5.1.1 Faults in machine 41 5.1.2 Faults in raw material 41 5.1.3 Faults in product 41
5.2 Faults of dyeing 42 5.2.1 Faults in machine 42 5.2.2 Faults in raw material 42 5.3 Sizing Faults 42 5.4 Weaving Faults 42
Chapter 6: Denim washing
6.1 Introduction 43 6.2 How does washing create unique look 43 6.3 Processes involve in Denim washing 43 6.3.1 Dry process 43 6.3.2 Wet process 47 6.4 Types of denim washes 48 6.4.1 Chemical wash 48 6.4.2 Mechanical wash 56
6.6 Spraying 60
6.7 Whiskering 61
6.8 Softening process 63 6.9 Machine use for denim 67 6.10 New development 69 6.11 Value edition 71
Chapter 7
7.1 Conclusion 74
1.1 INTRODUCTION
Denim and jeans - where do the names come from? The word jeans come from a kind of material that was made in Europe. The material, called jean, was named after sailors from genoa in Italy, because they wore clothes made from it. The word 'denim' probably came from the name of a French material, serge de nimes: serge (a kind of material) from nimes (a town in France),
1.2 BACKGROUND
We have interest in denim washing.
Denim has fewer difficulties in process as compare to other dyeing process.
Few industries work on this topic so that‟s why we decide to do the topic and we will try to optimize the process and try to invent new washes or finishes in denim.
Denim is a universal fabric, one that covers all age groups, races and social divides that‟s why we think it will have high demand in the future and this is also the point of our attraction for this topic.
1.3 HISTROY OF DENIM:
In fashion history, jeans and denim history continues to baffle. No one truly knows the perfect answer to where jeans began. As so often happens fashions often emerge together in various parts of the world and are the result of the sudden availability of a new fabric, cloth, dye or technique. But we do know that the phrase denim jeans are thought to derive from several sources. No one is totally certain where the words come from. A majority of source books suggest that denim derives from the English translation of the South of France French phrase 'serge de Nîmes'. Denim fashion history is thus associated with Serge de Nimes.
When talking about denim the name Levi´ s is one of the first to be mentioned. Levi´ s which stands for Levi Strauss is normally called the forefather of jeans. When tracing back the history of these trousers to its origins it is true that Levi Strauss played an important role concerning their development and distribution but he had also other inventive business partners.
Levi Strauss found out that the gold diggers´ hard work in the mines made their clothes get worn out very quickly and he produced stout working trousers out of the sail cloth he had taken with him which he called „half overalls“. When he continued producing these trousers he used cheap cotton fabrics coming from Genova. The name of the town of Genova was modified into „jeans” in the American slang. At the end of the sixties of the 19
th
century he replaced the brown sail cloth by an indigo-dyed, wear resistant cotton fabric coming from France. The name of this fabric was „Serge de Nimes“. Serge is the French. Expression for a combined twill and Nimes is the French town where the fabric comes from. The fabric´s name Serge de Nimes was quickly turned into „Denim“ in American colloquial language. By applying this indigo-dyed combined twill the first jeans out of Denim was almost born or better sewn. The application of metal rivets for jeans is due to the Polish emigrant Jacob W. Davis, also called AJacob Youphes. Although the working trousers out of Denim were stout they had a tendency to get worn out where the pockets were. Jacob Youphes mended the trousers with a needle and thread. One day a customer inspired him to repair the torn off pockets with the help of rivets. Under the management of Levi Strauss the jeans were now produced in series. Since the trousers were so stout not only the gold diggers liked them but which is not surprising in America? The cowboys appreciated them very much, too. When the trousers were applied as working trousers for cowboys, however they got worn out at the crotch tip. This was no problem for Levi Strauss and Co. since they reinforcedthe trousers again with metal rivets at the crossing point of the four seams at the crotch tip.
About 1947 denim made a break-away from work clothing image, chiefly in the area of sportswear and rainwear and an occasional appearance in high fashion collections as a "different-looking" evening dress. In 1970 American youth adopted denim as their favorite fabric. Part of a "back to nature" movement that emphasized ecology and the natural denim being a fabric created from a natural fiber was a primary factor. Since 1960 the jeans business has undergone an explosive transformation, from a source of tough, cheap clothing for cowboys, blue-collar workers and penniless youth into a fashion conscious market for a widening mass of people of almost all ages.
1.4 LITERATURE REVIEW
The studies related to the denim manufacturing and processing is available to understand the process sequence and achieving various washing effects of denim.
Processes for producing yarns dyed with indigo have been in use for thousands of years. The original batch methods for dyeing yarn skeins have been replaced for the most part with continuous dye ranges that can produce thousands of pounds of dyed yarns each hour. Different experiment have been done before on denim washing, denim dyeing they are done internationally as well as locally in our country in which few are discussed below.
In past, stone (pebbles) are use for washing which is known as stone wash but now a days stone (pebbles) are replaced by rubber balls because stone damaged the fabric during the washing process.
Another experiment was done internationally and primary object of the invention is to provide a method of treating denim fabric in plain fabric form or in garment form to economically produce stonewashed denim fabric of various different shades colors without multiple steps, expensive equipment, or large inventories of fabrics and dyes. Another object of the invention is to economically provide stonewashed denim fabric of different shades and colors.
In earlier work many denim washes has been created in which some denim washed names are given below:
1 ACID WASH 2 ENZYME WASH 3 BLEACH WASH 4 STONE WASH
Companies that “finish” jeans by washing them or distressing them for a worn-in look. Most major jeans manufacturers use several different laundries that specialize in different finishes. The main techniques used include simple washing, stonewashing, which uses an abrasive-bristled Tonello machine, sandblasting, laser burning, or applying enzymes to simulate “cat‟s whisker”-wear line, and sandpapering by hand.
Our seniour students also worked on denim washing and they also tried to developing the new techniques in denim washing but unfortunately they were not success in developing new techniques.
1.5 AREAS OF STUDY:
In this project we will study denim washing along with its weaving and its dyeing process and we will try to optimize the current methods but we will focus deeply on denim washing and its finishing.
WARPING
The first process in the manufacturing of denim is warping.
2.1 INTRODUCTION
Warping is the process of transferring multiple yarns from individual yarn packages onto a single package assembly. Normally, yarns are collected in a sheet form where the yarns lie parallel to each other and in the same plane onto a beam, which is a cylindrical barrel with side flanges. This is known as beam warping. For ball warp denim, the yarns are brought together and condensed into a rope before being wound onto a relatively short cylindrical barrel (sometimes called the shell or log) that has no end flanges.. In both cases, the supply yarn packages are placed on spindles, which are located in a framework called a creel.
2.2 Ball Warping :
In ball warping (Figure 5), 250 to 400 yarn ends are pulled from the creel. The yarns then pass through a comb-like device (sometimes called a hack or reed), which keeps each warp yarn separate and parallel to its neighboring ends. At intervals of every 1000 or 2000 yards (or meters), a lease string is placed across the sheet of warp yarns to aid yarn
through a funnel-shaped device called a trumpet or condenser, which collapses and condenses the sheet of yarn into rope form. This device is located at the base of the warper head and traverses back and forth, guiding the newly formed rope of yarn onto a log. The rope must be wound at a constant tension to keep the yarns from tangling.
2.3 Beam Warping
Beam warping maintains the yarns in an open sheet form and winds the yarns parallel to each other onto a slightly wider flanged beam. These yarns will not go through the rope indigo dye range, but are left “natural” and will end up either slasher dyed or in an un-dyed fabric, which can later be piece un-dyed, garment un-dyed, or left natural. Another option would be to beam dye the yarns using a dye other than indigo.
2.4 COMPONENTS OF MACHINE
• Creel • Rods • Chain System • Control Devices • Sensors • Head stock • Expansion Comb• Dust and fly accumulation unit Showering assembly
2.5 PROCEDURE OF WARPING:
The creel stand has maximum capacity of five cones per stand.
The yarn from the cones is unwounded and passes from rod by cross wound, holed by a catcher guided to the tensioning zone when cone rotates anticlockwise. There are three types of tension in warping i.e. catcher tension, rod tension, and sacker tension. Magnetic tensioner is used for yarn tension.
Then the yarn comes to the winding zone or headstock. Combs straighten the yarns towards pressure drum, which supports beam, and yarns in an alignment so that each and every yarn end can wound separately. Static charges due to friction of yarns on metal surface cause static charges, which are removed through an anti static device. Then the yarn is wounded on beam in this way for a required length if beam is changed after one filling of beam then knotting of yarns is made. Similarly if cones are finished on one frame side then trolley system of cone changing is used in this way chains rotates the whole frame of empty side and new filled side of frame is forwarded again knotting is done between the new cones yarn and already winded yarn. Extra yarn is then removed through cutting. Sensors sense any type of yarn breakage and in case of yarn breakage knotting is done.
DYEING
3.1 INTRODUCTION
Dyeing is a process in which we impart colour into the fabric. All commercial textile dyeing processes take place by the application of a solution or a dispersion of the dyes to the textile material followed by some type of fixation process. The dye solution or dispersion is almost always in an aqueous medium. A major objective of the fixation step is normally to ensure that the coloured textile exhibits satisfactory fastness to subsequent treatment in aqueous wash liquors. Dyeing is mainly depends on the type of fabric, structure of fabric and the properties of dyes.
3.2 CLASSIFICATION OF DYES
For our convenience we make classes of dyes, due to these classes the application of dyes is much easier. The classifications of dyes are as follows:
• Direct Dyes • Reactive Dyes • Sulphur Dyes • Vat Dyes
3.2.1 DIRECT DYES
Direct dyes have been used to dye cellulose for over 100 years. Because of the simplicity of application and great choice of products available, direct dyes are a popular dye class. Direct dyes ranges from moderate to poor in wash fastness. Light fastness varies from poor to excellent depending on the particular dye. Direct dyes depend on secondary forces such as hydrogen bonds and vander waals forces to bond with cellulose fibres. Since secondary forces are relatively weak. Therefore, direct dye molecules have relatively high molecular weights, typically 400 to 1200. The great majority of direct dyes are azo structures.
3.2.2 REACTIVE DYES
Reactive dyes contain groups that react with the hydroxyl groups in cellulose. The reaction between a reactive dye and the fibre produces a covalent bond. By their nature reactive dyes also react with water. Dye which reacts with the fibre is said to be “fixed” to the fibre. Dye which reacts with water is said to be “hydrolyzed”.
Fixation Reaction
Cell – CH2 – OH + DYE – X Cell – CH2 – O – DYE + HX
Cellulose reactive dye dyed fibre acid X=reactive group
Hydrolysis reaction
H – O – H + DYE – X DYE – OH + HX
Dye molecules which react with the fibre and become fixed have excellent fastness to washing because of the high strength of the covalent bond. Dye molecules which are hydrolyzed may be weakly attached to the fibre and if not washed out at the end of the dye cycle have very poor wash fastness.
3.2.4 SULPHUR DYES
Sulphur dyes are widely used on cotton mainly because they are economical to use. They have good to excellent wash fastness and good light fastness in dark shades. Light fastness of pale shades is poor. Sulphur dyes are usually dull in shade since the molecular structures are complex. As a class, the sulphur dyes are not resistant to chlorine containing bleaches.
Chemical nature of sulphur dyes
3.2.5 VAT DYES
Vat dyes are mainly on cellulosic fibres, but some can be applied to protein fibres. They usually have outstanding colourfastness properties. Vat dyes are more expensive and difficult to apply than other classes for cellulose such as directs sulphurs, and reactive. Indigo is a special case in the vat dye class. Indigo is attractive for its pleasing blue colour and for the unique fading characteristics of garment dyed with it.
Vat dyes are characterized by the presence of a keto group. Vat dyes in keto form are water insoluble pigments.
Reactions of Indigo Dye
THE SUBSTANTIVITY AND DYEING CHARACTERISTICS OF
VAT DYES FOR CELLULOSIC FIBRES.
BASIC STEPS IN THE DYEING PROCESS
The dyeing of cellulosic materials with vat dyes follows a four-step sequence: 1. Preparation of the vat containing the leuco forms of the dyes;
2. Dyeing of the material, in which the fibers absorb the water-soluble leuco compound;
3. Oxidation of the absorbed leuco compound back to the parent pigment inside the fibers
4. Soaping of the dyed material to remove pigment loosely adhering to the fiber surfaces and to develop the true shade and fastness properties.
3.3 DENIM DYEING:
The classical jeans were produced out of indigo-dyed Denim fabric. The special character of this fabric only the warp thread is dyed makes it necessary to carry out dyeing in yarn form. The yarns applied for Denim were exclusively produced on ring spinning machines in former times. The development of OE (open end) yarns by applying smaller rotors with a spinning speed of up to 200 m/min - has led to the application of OE rotor yarns both for warp and weft. The yarns applied for weaving must be of high quality: a high fiber for strength, regularity as well as a small part of short-stapled cotton fibers belong to the basic features of the denim yarn. For regular jeans qualities the warp yarns are spun in a fineness of 50 to 90 tex, for the weft yarn the fineness ranges are mainly 75 to 120 tex. If Denim is made out of Tencel or Modal especially for jeans shirts the finenesses are up to 25 tex.
Indigo, sulphur and indanthrene are mainly used in the dyeing process. Two methods are applicable for continuous dyeing with indanthrene dyes: rapid dyeing and vat dyeing. While processing the basic colored denim, reactive dyes are used and fixed with hot caustic soda solution. The dyeing process is mainly influenced by the dyestuff characteristics, dyeing temperature and necessary chemicals used in the process. Indigo dye is the most popular choice as it has good depth of shade and suitable rubbing and washing fastness. When cotton yarn is dyed with indigo, it leaves a ring-dyeing effect, because of which the outer layer of warp yarn is coated with indigo, and the core of the yarn remains undyed. This gives the denim garment a unique „faded look‟ and a rich blue shade after repeated use and wash. Originally, the warp yarns or ends were put through the dye bath side by side to form a sheet of yarn, which passed continuously through several dye baths, squeeze rollers or airing sequences. However, if there were breaks in the yarn (and there would be, as each yarn had to take the tension of being pulled through these processes virtually on its own), the dyeing process had to be stopped. The yarns would be then mended, or else it would lead to very bad tangling. These stoppages would in turn cause large shade variations, and the yarn breaks would show up as bad faults in
the fabric. Now, an infinitely more efficient system has been introduced. Special attention shall be paid here to Indigo, the „king of dyestuffs” since it plays an important role in obtaining the jeans effect. Indigo belongs to the category of water-insoluble dyestuffs. It was first mentioned in a book 13 BC; at that time the name Indian blue indicated the country the color came from. It is said to have been used for dyeing in India and China 2000 years BC already.
The Indigo plant is used for preparing Indigo
Nowadays, yarn dyeing with indigo is done continuously. Here the various dyeing processes with different concentrations of chemicals as well as the subsequent yarn sizing exert an influence on the quality and the appearance of the ready fabric. There are two processes in the practice for continuous dyeing:
• · Rope Dyeing
3.3.1 ROPE DYEING
Indigo Rope Dyeing When dyeing according to the rope dyeing or cable dyeing method.350 - 400 warp threads are bound on the ball warper to very thick cables of 10 000 - 15 000 m length. On the continuous dyeing installation, 12 to 36 cables are led side by side, wetted, dyed and dried after the dyeing process on cylinders and put into cans. Then the cables are dissolved to warps on the long chain beamer. The warps are added to the sizing machine, sized and then led together to warp depending on the total numbers of threads. In practice, this method has proven to be very good through obtaining an optimum indigo dyeing. However it is important that the cables have a constant tension in order to avoid warp stripes. The disadvantage compared to other methods is that yarn breakages do occur more often. Size of the dyeing unit is between 60 - 80 m. Normally, 6 dyeing vats are in use. There are nevertheless variations with 3 to 8 dyeing vats.
3.3.2 SLASHER DYEING
Indigo Sheet or Double Sheet Dyeing (Slasher Dyeing).When dyeing according to the sheet dyeing method, instead of cables the warp threads are fed to the machine parallel next to each other. These are much smaller compared to the rope dyeing machines. Another advantage is that the cables don‟t need to be open after dyeing. Moreover, each yarn wets much faster and in this way reduces the dipping and wetting times during dyeing. All in all, each thread has a larger surface compared to a dyeing cable and this requires somewhat more hydrosulphite to prevent a premature oxidation of the indigo.
Whereas during rope and sheet dyeing the yarns are always led in succession to the dyeing baths, the fabric of the loop dye method is led several times through the same dyeing bath. The machine is then much shorter and the hydrosulphite consumption is lower. Depending on the number of dyed passages and the concentration of indigo in the dyeing vats, different dyeings of the yarn. . [3]
WORKING PRINCIPLE OF SLASHER
Warp beams are brought to the dyeing and sizing section in sheet form as per requirement. The warp sheet is taken to wetting tank (like mercerize, semi mercerize and causticize tanks depends upon the dyeing methods) which swells the fiber and increases its dye uptake. It is then taken to a hot washing tank whose temperature is maintained at 85
0
C. It is then taken to cold washing tank whose temperature is maintained at 60
0
C. Warp sheet is then taken to dyeing tanks where dye is reduced to soluble leuco form by using sodium hydrosulfite, yarn is then contacted with the reduced dye, and the dye is adsorbed by the fibers. The fixed leuco indigo in the yarns of the warp sheet was oxidized to form pigment during transport of the warp sheet in the air space following the dwelling chamber, taking approximately 60 seconds. It is taken to two hot washing tanks for fixation. Following rinsing, warp sheet is dried on cylinders dryers prior to the application of sizing agent.
OXIDATION REACTION Na 2S2O4 + O2 + 2NaOH → Na2SO4 + Na2SO3 + H2O + C16H10O2N2Na2 + ½ O2 + H2O + Sodium Hydrosulfide C 16H10O2N2 + 2NaOH Oxidized indigo
During the slashing process, the sheet of yarns is passed through the size box which contains the hot water solution or mixtures of sizing agents. The yarns pick up the required quantity of size solution in the size box, excess size is squeezed off as the yarns pass through squeeze rolls. After the size box, the yarns go through the dryer section. The wet yarns are dried by using drying cylinders. Cylinder drying is done using steam heated hot rolls. The Teflon coating is done on all the cylinders to prevent sticking of yarns. Accumulator stores 150 meters of warp sheet. Due to the nature of sizing, the yarns in the sheet may be stuck together at the exit of the dryer section. They are separated into individual sheets by leasing rods and individual ends of yarns are separated by passing through comb then the yarns are wound on to a loom beam for weaving.
3.4 DIFFERERENCE BETWEEN SLASHER AND ROPE DYEING
ROPE DYEING
SLASHER DYEING
Warp yarns are assembled on the ball warper to form a rope.
Warp yarns are directly wound on a beam in the form of a sheet.
Ropes are drawn through dyeing range side by side.
Dyeing is done in sheet form
After dyeing they are dried on a drum drier and deposited in cans. The ends are spread out on long chain beamer Or on a rebeamer, and the yarn sheet is wound onto warp beams. These beams are then taken to sizing. After sizing they are dried and assembled on the weaving beam.
After dyeing the warp sheet is dried on the same machine in continuous process by drying cylinders and then sizing is done on the same machine and after drying it is wound on a weaver beam
Good depth of shade is achieved Depth of shade is not good In rope dyeing we have very high
productivity but the limitation is that it is
In Slasher dyeing productivity is less but it is feasible for short lots.
very expensive for short lots.
It can only run for coarse yarn as the tension on rope breaks the yarn
It can run for fine yarns too
Time consuming processes are rebeaming and then sizing
Rebeaming is not required and sizing is done after dyeing.
As the dye bath is less exposed to air so dye is affected less.
Setting up or stabilization of the dye baths is affected faster.
The oxidation time is greater for fixation The immersion and oxidation times are much shorter
The wetting time is greater and so dye is applied uniformly
Owing to the paralleled warp threads, the wetting process is shorter and a wetting trough may be adequate.
The rope dyeing machine is much expensive than Slasher.
The sheet dyeing machine is smaller than a rope dyeing machine, which means that the prime costs are lower
Rope opening is avoided Warp sheet entanglement is a danger
Bottoming:
In this case another dye is applied before dyeing with indigo. First the warp sheet is dyed with sulfur and then it is washed and then dyed with indigo.
Topping
: In this case the warp sheet is dyed with indigo in start and then itis washed and then it is dyed with another dye (normally with sulfur).
Bottoming indigo Topping:
In this case the warp sheet is firstly dyed with some dye and then after washing with indigo and then after washing with other dye like sulfur.Washing is done after each bath in order to remove unfixed dye. Dyeing of indigo occurs at low temperature and that of sulfur at high temperature. Firstly the warp sheet is dipped in the dyeing liquor and then airing is done in order to do fixation as indigo and sulfur dyes are in reduced form in liquor than they are oxidized by giving air. Which is necessary because if airing is not proper than immature oxidation occurs. For this purpose an airing zone of about 40 m is provided after each bath. The airing process is also known as dwelling time.
3.5 COOKING TANKS AND DOSING SYSTEM:
A color kitchen is also known as cooking tanks. Five cooking tanks are also provided with the machine which is used for the preparation of liquor for pre-treatment, dyeing and sizing. They are connected with the machine via dosing system. The computer-controlled
dosing system for dyestuff and chemicals is the heart of the machine. Indigo vat, hydrosulphite and caustic soda are continuously added according to calculated quantity indications and depending upon speed. Color UN levelness owing to fluctuations in bath concentrations does no longer occur. Owing to the high circulation rate of the dye liquor in two circuits, local bath concentration differences are avoided. The metering control stores the required adjustment parameters and guarantees a high level of process reliability and reproducibility.
The used dyes can also be preserved with the help of two storage tanks on the machine. Useless dye is drained easily from the tanks with the pipes connected at there bottom.
3.6 AFTER-WASHING PROCESS AND DRYING
After dyeing of the warp sheet washing is done in order to remove the unfixed liquor from the warp sheet. The two or three hot washes are done after the dyeing. And then it is dried on the assembly having 07 drying cylinders.
3.7 SIZING
Although the quality and characteristics of the warp yarns coming out of the winding, warping and dyeing processes are quite good, they are still not good enough for the weaving process for most of the yarns. The weaving process requires the warp yarns to be strong, smooth and elastic or extensible to certain degree. To achieve these properties on the warp yarns, a protective coating of polymeric film forming agent (size) is applied to the warp yarns prior to weaving; this process is called slashing or sizing.
The main purposes of slashing are as follows: • To increase the strength of the yarns
• To reduce the yarn hairiness that would cause problems in weaving process
• To increase the abrasion resistance of the yarn against other yarns and various machine elements
• To reduce fluff and fly during the weaving process for high speed weaving machines.
One sizing tank is provided after the drying zone. The capacity of the size box is about 400 liters. Sizing material is provided automatically by dosing system or it can be manually added.
3.8 Drying Zone
After the size box the yarns go through the dryer section. The wet yarns are dried by using cylinder drying. Cylinder drying is done using steam heated hot rolls called the drying cylinders. The cylinders are coated with Teflon to prevent sticking of the yarns on the cylinders. The drying zone contains 14 cylinders.
3.9 ACCUMULATOR:
Accumulator is also known as compensators. After drying two accumulators are provided on the machine. Whose function is to minimize chance of stoppage of machine because of the change of beam on the head stock and insertion of rods in the leasing zone they accumulate the extra warp when the speed is reduced from the headstock by moving assembly to upward direction as shown in figure below
When the head stock is moved with a greater speed the excess warp is removes from the accumulator.
3.10 LEASING ZONE
Due to the nature of sizing, the yarns in the sheet may be stuck together at the exit of dryer section. Therefore they are separated into individual ends using leasing rods. The individual sheets of yarns from each section beam are separated.
3.11 EXPANSION COMB
Pins in the expansion comb separate the yarns within each sheet. With the expansion comb the warps are spread according to the required width of the weaver‟s beam.
3.12 BEAMING
The yarns are wound on to weaver‟s beam at the headstock. Maximum beam width of 4000 mm can be used, usually 3600 mm is used. A pressing roller is pressing the warp yarn for uniform tension winding. A guide roller guides the yarns to the weaver‟s beam. A pressing roller is pressing the warp yarn for uniform tension winding. A machine speed of 100-110 m/min. is used
3.13 TRANSPORTATION OF BEAMS:
After the winding of dyed warp beams the from the head stock the samples of the yarn are taken to laboratory for testing and then it is transported to the weaving department.
WEAVING
4.1 INTRODUCTION
The process of producing a fabric by interlacing warp and weft threads is known as weaving. The machine used for weaving is known as weaving machine or loom. Weaving is an art that has been practiced for thousands of years. The earliest application of weaving dates back to the Egyptian civilization. Over the years, both the process as well as the machine has undergone phenomenal changes. As of today, there is a wide range of looms being used, right from the simplest handloom to the most sophisticated loom.
4.2 BASIC WEAVE DESIGNS
There are three basic weaves:
• Plain weave
• Twill weave
4.3 Weaving of Denim Fabric:
Denim is a fabric traditionally woven with what is known as a twill weave. This is simply a weaving pattern that produces parallel diagonal ribs.
The weaving process interlaces the warp, which are the length-wise indigo dyed yarn and the filling, which are the natural-colored cross-wise yarn. The warp thread is in the form of sheet.
In denim, the warp-faced twill pattern calls for passing the weft yarn over one and under two (1/2), or over one and under three warp (1/3) yarns. Because there are fewer lacings in twills than in plain weaves, the yarns are freer to move when being worn resulting in a fabric that is both flexible and resilient.
The weft thread is inserted between two layers of warp sheets by means of a suitable carrier, such as Shuttle, Projectile, Rapier, Air current, Water current, etc. The selection of carrier depends upon the type of weaving machinery used. The two different technologies available for weaving machines are - Conventional Shuttle Weaving System which is done by Ordinary Looms or Automatic Looms; and the Shuttle less Weaving System which is done by Airjet, Waterjet, Rapier, or a Projectile weaving machine. The Conventional Shuttle loom results in lesser production due to slow speed and excessive wear and tear of machinery. As such, now denim is generally woven through Shuttle less Weaving System namely, Airjet looms, rapier looms or projectile looms.
The most common twill used for jeans is a 3x1. A 2x1 twill is used in lighter weight denim.
The yarns used in making denim have a very high twist, a process which gives the yarn much greater resistance both to tensile stress and to abrasion.
4.4 Typical Denim Constructions, Weaves, and Weights
The classical construction of a bottom weight 14.5-ounce denim is 60-64 warp yarns per inch and 38-42 filling yarns per inch. The number of warp yarns per inch is sometimes referred to as the fabric sley. The weight is influenced by the size of the yarn used, the fabric weave design, and the fabric tightness. Also influencing the fabric weight is the amount of size left on the finished fabric. Other denim fabrics and denim “look-a-likes”
may vary in construction from 52 to 70 warp yarns per inch and from 36 to 52 picks per inch. As a rule, denim is woven as 3/1 twill, 2/1 twill, 3/1 broken twill, or 2/2 broken twill. The weights of these finished fabrics can vary between 3.5 and 16.5 ounces per square yard. The weight of the fabric usually determines what the final garment application will be:
Numerical notations for different denim designs, such as 3/1, denote what each warp yarn is doing relative to the filling yarns that it is interlacing with. In this case, each warp yarn is going “over” three picks and then “under” one pick. This would be verbally stated as “3 by 1” twill or “3 by 1” denim. At the next end, moving to the right, the same sequence is repeated but advanced up one pick. This advancing upward sequence continues, giving the characteristic twill line. In this case, the twill line is rising to the right, and the fabric is classified as a right- hand twill weave. If the twill line is made to rise to the left, then the design is left-hand twill. Broken twills are designed by breaking up the twill line at different intervals thus keeping it from being in a straight line.
Left Hand Twill:
This refers to the direction that the denim is woven. Left hand twill denim is softer to the touch than right hand twill, and was originally used by Lee denim. Left hand twill is easy to spot, as the weft threads appear to move upward and to the left as opposed to upward and to the right.
Right Hand Twill:
This refers to the direction that the denim is woven. The opposite of Left Hand twill, this weave is much more common, as almost all jeans are woven with right hand twill. The weft (filler) threads will be visible in upward-right diagonal lines on right-hand twill jeans.
Broken Twill:
Instead of the twill running to the right or left, broken twill jeans (traditionally considered the cowboy-preferred denim) contain no distinct direction of weave. The weave is instead
alternated right and left - the end effect resembles a random zig-zag. Broken Twill was designed to combat the twisting effect that was a characteristic regular twill (and considered a 'fault' by many at the time). By going on both directions, the tension in the yarns is balanced in Broken Twill.
4.5 Non-conventional Denim Fabric Constructions
Indigo-dyed yarns have been woven in plain weaves known as chambray, oxfords, baskets, herringbones, bedford cords, and combinations of 3/1 and 1/3 twills. Jacquard designs and dobby weaves have also been incorporated into denim designs to produce new looks and textures.
Twill Weave
Twill Weave is produced in a stepwise progression of the warp yarn interlacing pattern. The interlacing pattern of each warp yarn starts on a different filling yarn and follows the same formula. These results in the appearance of a diagonal line called twill line in the fabric, which is then characteristic of this design. Depending on the direction of the twill line, the twill weaves are called right-hand or left-hand twills. The sum of the digits in the formula determines the unit cell of the design, which also gives the minimum number of harnesses, requires weaving the design; at least three harnesses are required for a twill weave. Common twill, Steep twill, Reclining twill and Broken twill are the different variations of the twill weave.
4.6 SHEDDING SYSTEM:
There are four shedding systems used to provide manipulation to the warp yarns:
1. Crank Shedding 2. Cam Shedding 3. Dobby Shedding 4. Jacquard Shedding
4.6.1 CRANK SHEDDING:
This is the simplest shedding system. In this system, the crankshaft of the weaving machine provides the harness motion. This system is used only for plain weave and its derivatives.
4.6.2 CAM SHEDDING:
A typical cam system can handle weave patterns with up to 14 different harnesses. Cam shedding mechanisms are relatively simple. A pair of cams is sufficient to weave plain fabric. A cam is a disk that transforms a rotational motion of its own to a reciprocating motion of a follower. The transfer is done by means of the cam‟s edge or a groove cut in its surface.
4.6.3 DOBBY SHEDDING:
Dobby mechanisms are more complicated than cam systems. They are normally built to control up to 30 harnesses. Picks per repeat are virtually unlimited in dobby. Basically there are two separate functions in dobby mechanism: 10 power transmission, 2) connection and disconnection of the harnesses to from the power source at the proper time. Dobby mechanisms are classified as negative, positive and rotary dobby. They can be mechanical or electronic.
4.6.4 JACQUARD SHEDDING:
Jacquard Shedding offers unlimited patterning possibilities. The Jacquard machines offer the highest level of warp yarn control. This versatility is due to the separate control of each warp end or groups of similarly interlacing warp ends within the pattern repeat across the fabric width. They enable the most sophisticated patterns, such as pictures, to be produced in the woven fabrics. Jacquard machines can be mechanical or electronic with single lift or double lift mechanisms; the new machines are all double lift. Most Jacquards heads generally are equipped to handle over 2000 harness cords or hooks with pattern repeating on about on about 9000 picks and multiple heads can be employed over a single weaving machine to increase the weave pattern capability. Jacquard systems are placed on top of the weaving machine.
FILLING INSERTION:
After each shed change, the filling yarn is inserted through the shed. It is possible to select and insert different filling yarns one after another.
Weaving machines are usually classified according to the filling insertion mechanism. The major filling insertion systems used today are rapier, projectile, air-jet, and water- jet, which are called shuttle-less weaving systems.
4.7 CLASSIFICATION OF WEAVING MACHINES:
Weaving machines are classified according to their filling insertion mechanism. The classification is as follows: 1. Shuttle 2. Shuttle-less • Rapier • Projectile • Air-Jet • Water-Jet
4.7.1 Shuttle Weaving
In shuttle weaving, a shuttle that traverses back and forth across the loom width, inserts the filling. Shuttles can be made of wood or plastic. Filling yarn is wound on the quill and the quill is placed in the shuttle. As the shuttle move across the loom, the filling yarn is unwound from the pirn and lay in the shed.
4.7.2 Shuttle-less Weaving:
Rapier Weaving
In Rapier weaving, a flexible or rigid solid element, called rapier, is used to insert the filling yarn across the shed. The rapier head picks up the filling yarn and carries it through the shed. After reaching the destination, the rapier head returns empty to pick up the next filling yarn, which completes the cycle. A rapier performs a reciprocating motion.
1. Single Rapier Machines: A single, rigid rapier is used in these machines. The rigid rapier is a metal or composite bar usually with a circular cross section. The rapier enters the shed from one side, picks up the tip of the filling yarn on the other side and passes it across the loom width while retracting. Therefore, a single rapier carries the yarn in one way only and half of the rapier movement is wasted. Also there is no yarn transfer since there is only one rapier. The single rapier‟s length is equal to the width of the loom.
2. Double Rapier Machines: Two rapiers are used in these machines: one rapier, called the giver, takes the filling yarn from the yarn accumulator on one side of the loom, brings it to the center of the machine and transfers it to the second rapier which is called the taker. The taker retards and brings the filling yarn to the other side. Similar to the single rapier machines, only half of the rapier movements is used for filling insertion
Projectile Weaving
Projectile weaving machines use a projectile equipped with a gripper to insert the filling yarn across the machine. The gripper projectile draws the filling yarn into the shed. The Projectile glides through the shed in a rake- shaped guide. Braked in the receiving unit, the Projectile is then conveyed to its original position by a transport device installed under the shed.
Air-Jet Weaving
Air-jet weaving is a type of weaving in which the filling yarn is inserted into the warp shed with compressed air. Air-jet system utilizes a multiple nozzle systems and a profiled reed. Yarn is drawn from a filing supply package by the filing feeder and each pick is measured for the filling insertion by means of a stopper. Upon release of the filling yarn by the stopper, the filling is fed into the reed tunnel via tandem and main nozzles, which provide the initial acceleration. The relay nozzles provide the high air velocity across the
weave shed. Profiled reed provides guidance for the air and separates the filling yarn from the warp yarn.
Water-Jet Weaving
A water-jet weaving machine inserts the filling yarn by highly pressurized water. The relative velocity between the filling yarn and the water jet provides the attractive force. If there is no velocity difference, then there would be no tension on the yarn results in curling and snarling of the yarn. Water-jet weaving machine can only be used for hydrophobic fibers.
Beat-up
When the filling yarn is inserted through the shed, it lies relatively far from its final position. This final position is called the fell, which is the imaginary line where the fabric starts. Beat-up is the process of pushing the last inserted filling yarn to the cloth fell by using a device called reed. The fabric is not formed until beat-up occurs. Reed is a closed comb of flat metal strips. These metal strips are uniformly spaced. The spaces between the metal strips are called dents. The reed is also used to control the warp yarn density
more warp yarns in each dent and pushes them to the cloth fell. After beating up the filing yarn, the reed is withdrawn to its original rest position before the insertion of the next filling. Reeds are identified by a “reed number‟ which is the number of dents per unit width. Specifying the number of ends per dent with a certain reed number dictates the density of warp yarns in the fabric. Reeds are of two types according to their shape; Regular reed and Profiled reed (used in air-jet weaving). Reed can be single or double. A double reed has two rows of metal strips. The rear row starts from the middle of the first dent of the front row of the metal strips. The double reed is used in terry weaving.
Fabric take-up
As the fabric is woven, it should be removed from the weaving area. This is achieved by the take-up motion. The fabric take-up removes the cloth at a rate that controls filling density (picks per inch).
LOOMING
Looming covers the process involved in warp preparation after sizing up to setting them to loom. The process can be shown as follows:
Drawing-in → Warp Tying → Loom
During slashing, the exact number of warp yarns required in fabric is wound on to the loom (or weaver's) beam. The warp ends are then passed through the drop wires of the warp stop motion, the heddles of the harness frames and the dents at the reed. This can be achieved by drawing -in or tying -in, the choice depending upon whether or not the new warp is different form the warp already on the loom.
DRAWING-IN
The process of drawing every warp end through its drop wire, heddle eye and reed dent can be performed manually or by means of automatic machines. In both case, a length of warp yarn, just enough to reach to the other side of the frame, is unwound. Leasing (i.e. selecting warp) of the warp at this stage simplifies the separation of the yarns. Then they are threaded through drop wires heddle eyes and reed dents. The automatic drawing
TYING-IN
When fabric of a particular type is being mass-produced, the new warp beams will be identical with the exhausted beams on the looms. Therefore, if every end on the new beam is tied to its corresponding end on the old beam, the drawing-in process can be omitted. Tying-in may be done by means of a small portable machine on the loom or as a separate operation away from the loom.
FAULTS IN DENIM PRODUCTION
5.1 FAULTS OF WARPING:
5.1.1 FALUTS IN MACHINE:
•
Stop motion does not work on creel and on warping drum as a result broken ends are not traceable for knotting.• Chain breakages
• If frictional drum should not be kept in a polished state, then thermal damages occur due to abrasion.
• Brake could be inefficient. • Sprockets are jammed.
• If comb do not move properly then there is a chance of cutting of comb due to friction with yarn.
• Tension supplied if varied it causes breakages or loosening in yarn. • If speed of warper increase than yarn sheet may break
5.1.2 FALUTS IN RAW MATERIAL:
• Neps• Long thick places (in case of non slub yarn) • Short thick places (in case of non slub yarn) • Thin places
• Count variation • Hairiness
5.1.3 FALUTS IN PRODUCT:
• Misalignment of yarn sheet if the yarn sheet is not properly adjusted • Uneven package density
• Too soft package winding
• Package could not be in uniform density
5.2 FALUTS OF DYEING:
5.2.1 FALUTS IN MACHINE:
• leakage of steam in drying cylinders• wear and tear of rollers if bearing is jammed
• Improper working of load cell on squeezing roller. Which causes entanglement of warp sheet as pressure is not properly distributed
• Faults in dosing system can cause serious problem of shade variation. • If the accumulator do not work properly than the machine is stopped. • If speed of the machine is kept greater than the yarn` s bearable strength
5.2.2 FALUTS IN RAW MATERIAL:
The main causes of the dye ability variations in yarn are:
• Immature fibres • Dead fibres
• Vegetable matter or other foreign matter • Wrong twist
• Bad splice • Neps
• Count variations
5.3 SIZING FAULTS:
• pressure rolls do not work properly • squeezing rollers do not work properly
5.4 WEAVING FAULTS:
• dropper will not fall• sensors do not work properly • Problem in electrical panel • Problem in electronic card • wear and tear of temple • if dust comes in nozzles
DENIM WASHING
6.1 INTRODUCTION:
Denim washing is the aesthetic finish given to the denim fabric to enhance the appeal and to provide strength. Much of the appeal of dry denim lies in the fact that with time the fabric will fade in a manner similar to that which artificially distressed denim attempts to replicate. With dry denim, however, such fading is affected by the body of the person who wears the jeans and the activities of their daily life. This creates what many feel to be a more natural, unique look than pre-distressed denim.
6.2 HOW DOES WAHING CREATE UNIQUE LOOK?
Washing of the denim cause it to fade which result its unique look. There are at least three fundamental reason that indigo dyed denim washes down to produce lighter and more attractive shades during washing.
the outer more heavy dyed yarn surfaces loses dyed through abrasion by stones, enzymes and chemical effect.
Indigo dye has intrinsic chemical instability to strong oxidizing agent such as chlorine bleach.
Some of the undyed fiber in the interior of the yarn migrate to the yarn surface diluting the color of the yarn.
6.3 There are two process involved in DENIM WASHING.
1. DRY PROCESS
2. WET PROCESS
6.3.1 DRY PROCESS:
It is called Dry Process because all the processes which are listed below is done in dry condition, in the other says we don‟t use any chemical including water in this process.
Following process are carried out in DRY process. Which are listed below?
1. Brushing 2. Hand whisker 3. Grinding Hand Grinding Wheel Grinding 4. Tagging 5. Clipping
BRUSHING or HAND SANIDING or 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.
In this department dyed garment (denim) is scrabbled or brushed using Emery paper. 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.
The garment is wear on the machine (horizontal or vertical machine) which have two legs is filled by air (air is directly come from the compressor).then we start brushing with the help of emery paper until our required effect is achieved. Different types of emery paper are used e.g 100,120,320,400 and 600 grain size. The selection of the emery paper is depend upon the fabric weight i.e. if fabric is light then we use emery paper of 320,400,600 grade, normally 320 grade of emery paper is used and for heavy fabric high emery paper of 100 and 120 are used. By brushing the dye is removed from the surface of the garment.
HAND WHISKER:
In this process the same machine is use as used in brushing. On Denim, whiskers/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.
GRINDING:
Edge distressing or grinding is the process of destruction on jeans form edges of the garment. When we look at old jeans we find it destroyed from the edges of pockets, fly area, belt and bottom. This used effect can be created on jeans by grinding and is of key importance in high fashion garments.
It include the following processes.
PATTERN MAKING:
In grinding first the pattern is make of different designs then these pattern is mark on the grinding areas in the garment with the help of chalk. by doing all these the grinding area on the garment is become visible.
PADDING:
This is the main process of grinding in which fabric is put on the plate, which have a rubber pad of same pattern or design which is already mark on the garment .then emery paper is rubbed against the garment which remove the yarn from the garment to get the desire effect. 100 grade of emery paper is use for this process.
HAND GRINDING:
This is the process in which garment is slightly damage by removing surface yarn with the help of hand grinding machine. Hand grinding is done on the small areas while padding is done on large areas. The effect of both process (padding and hand grinding) are approximately same.
Grinding is done of garments by pen type of stone tools. It can be done in mid of the wash process. In many workshops it is done before any wash process as first process after
stitching. Stone tools similar to grinders used in wood and stone industry are utilized to work on garments with a few amendments to their design.
Pen type tools are very affective for this art work but consistency is always a big question while dealing in production. They are not much effective in large quantity production units. Staff is to be very experienced and careful other wise it may damage the garment beyond requirement. To work on edges is very sensitive and any heavy destruction will open the edges and make the garment not to wearable. This aspect needs special care and supervision in industry.
WHEEL GRINDING:
In this process the edges of the garment like edges of the waist band, bottom hem, front pocket, back pocket and back pocket cover are grind using wheel grinding machine. In high production units it is usually done with fixed grinding machines where grinding stone wheals fixed on high speed electrical motors. Operators rub the edges to rotating stone wheal to get the effect. Again the risk of damage to extent where the edges get opend is there and to avoid it strict supervision and skilled staff is of key importance. This method is very time and cost effective and large quantities are always deal in this way.
TAGGING:
Tacking or more commonly tag pinning is a very in fashion style in denim garment in these days. Usually tag pin machines are used to attach tag pins to garment. The procedure is very simple and proceeds as; garment is folded on required area and tacked
through folds. Garment is folded on specified areas and the fold is locked by tag pins. Now the garment is processed in washer and a permanent fold appears after removal of tag pin. This is important that tag pin is removed when the garment is dried completely. The inner of the fold is dark in shade due to less exposure to mechanical rubbing and chemicals.
Area of Application :
This effect can be designed any where on the garment in different styles. Most favorite areas for tacking are on waistband, bottom hems, back pocket and front pocket corners etc
Tag Pin Tagging Machine
CLIPPING:
In this process the small areas of the garment is bound by using clips on the required areas (generally at the bottom hem) then garment is put in the oven and finally forward to the washing dept. for final effect.
6.3.2 WET PROCESS
It is called wet process because in this we use certain chemicals to obtain a desired result.
1. Pre-Treatment 2. Washing 3. Enzyme wash
4. Bleach wash 5. Stone wash 6. Sand Blasting 7. Tinting 8. Over dyeing 9. Spraying 10. Whiskering
PRE TREATEMENT
This is very first & basic step but most important step of washing. Here the fate of denim garment is decided that it‟s going to appear good or bad. Good Pre treatments avoid streaking, stiffness & color loss. This process removes impurities, starch & stains during handling of fabric. This step is also called desizing (Removal of Size applied during denim fabric making in weft yarn). All the woven fabric contains size on them due to reasons to strengthen the yarn for weaving. There are many types of sizes available in the market but they can be divided in two major groups.
1. Water Soluble (CMC or PVA based sizes ) and
2. Dissolvable sizes in water (Starch based). Starch based sizes are most commonly used due to cheap prices & readily availability.
Methods of Removing Sizes from Denim:
· Washing with High Alkaline agents ( i.e. Soda ash ) · Washing with High Acidic agents (i.e. Acetic acid )· Washing with Oxidative chemicals ( i.e. Hydrogen Peroxide )
· Enzymatic desizing with Alfa amylase .. This is eco friendly & convenient .
6.4 DENIM WASHES ARE OF TWO TYPES:
6.4.1. CHEMICAL WASHES:
- Denim bleaching - Enzyme wash - Acid wash - Tinting - Over dyeingDENIM BLEACH:
This in one an important step in washing denim & can be done by various bleaching agents.
a) Calcium hypo chlorite b) Sodium hypo chlorite c) Hydrogen peroxide d) Potassium permanganate
First two chemicals are commonly being used for every medium to vintage denim but when it comes to super vintage & light shade its advisable to use potassium permanganate bleach to cut the color faster till half way & then neutralize it & go with Liquid ( Hypo ) bleach to adjust the desired shade. This process helps to get Greyer cast & also protects the lycra/spandex, retain elasticity.
Hydrogen Peroxide is rarely used as bleaching agent when very less color loss required or if fabric is sulphur top. As it takes longer time to give desired effect.
Potassium Permanganate is also being used on 100% sulphur black denim fabric for bleaching/reducing agent to get unique effects. As it‟s not production friendly till laundry has very expertise team to handle this program, otherwise it will result in many shades & cast. Proper Neutralizations of bleaching process is very essential in order to get rid of fabric strength, bad smell from garment, yellowing & skin irritation etc.
In this process a strong oxidative bleaching agent such as sodium hypochlorite or KMnO4 is added during the washing with or without stone addition. Discoloration produced is usually more apparent depending on strength of the bleach liquor quantity, temperature and treatment time. It is preferable to have strong bleach with short treatment time. Care should be taken for the bleached goods so that they should be adequately antichlored or after washed with peroxide to minimize yellowing. Materials should be carefully sorted before processing for color uniformity.
LIMITATION
:
Process is difficult to control i.e. difficult to reach the same level of bleaching in repeated runs.
When desired level of bleaching reached the time span available to stop the bleaching is very narrow. Due to harshness of chemical, it may cause damage to cellulose resulting in severe strength losses and/or breaks or pinholes at the seam, pocket, etc.
Harmful to human health and causes corrosion to stainless steel.
Required antichlor treatment.
Problem of yellowing is very frequent due to residual chlorine.
Chlorinated organic substances occur as abundant products in bleaching, and pass into the effluent where they cause severe environmental pollution.
RANDOM BLEACH:
It is an uneven effect, some time also known as cloudy effect. In which denim is bleached indirectly via towel piece or cotton balls it produce more merge and cloudy effect cotton ball is more successful but cotton towel are some tome used to produce more cloudy effect.KMnO4 cannot be used with cotton balls/ribbons. It is only possible with hypochlorite. Black sulfur is not process able with hypochlorite as sulfur reacts vigorously with sulfur and pace of process cannot be controlled.
Procedure:
In this process we take bleaching agent in washing machine then we put small pieces of towel or cotton (raw cotton) then we will run the machine for few minutes until the towel soaked the bleaching agent. Then we drain the bleach after that we put the garments in the machine with towel pieces and run the machine until we get a required effect. We immediately neutralize the garment to prevent bleach spots or patches.
ENZYME WASH:
It is environmentally friendly wash. It involves the Application of organic enzymes that eat away at the fabric, i.e. the cellulose.
When the desired color is achieved, the enzymes can be stopped by changing the alkalinity of the bath or its temperature. Post treatment includes final rinsing and softening cycle. The effects produced by the cellulose enzyme are---
1. Use of cellulase making the seams, hems, and pockets more noticeable 2. Salt pepper effect is color contrast effect.
3. Faded garment with acid cellulase enzyme provides less color contrast in proportion to garment washed with neutral cellulase enzymes.
There are four kind of Enzymes available in market for Denim Laundry business.. Amylase …. Desizing
Cellulase …. For Salt & pepper effect , contrast
Laccase…. … bio bleaching
Catalase …… Peroxide killer
Enzyme is kind of protein that is obtained from fermentations method from naturally existing bacteria & fungi. The structure of Enzyme is a biological polymer and it can be found in every cell. Generally called as Cellulase & it works on cotton( Cellulosic fiber ) only. Enzyme are living organisms which will attack a specific molecular group.
There are mainly three kind of Cellulase being used for Denim washing , Neutral, Acid and Bio polishing Enzyme. Enzyme are very sensitive with parameters in washing cycle i.e, pH , Temperature & time. If any of these parameters are not up to the mark, result will not be accurate. The reaction of enzyme can be easily controlled, its biodegradable products, so they eco friendly. Bio Polishing Cellulase are being used to have protruded fiber removal from denim & oven fabric. This is also widely known as Anti pilling enzyme. Any Cellulase used in process must be cleaned/killed after the process completion by simply disturbing the parameters ie. By raising high temp. or raising pH to alkaline where no Cellulase withstand.
Cellulase are available in 3 categories 1. Neutral
2. Acidic
3. Hybrid enzymes.
Neutral enzyme gives better salt & pepper effect with very less back staining & its generally come sin powder form & also retains better strength of fabric than acidic Cellulase. Where as acidic cellulase give faster results but with too heavy back staining & cuts down the indigo color, also affects the strength of fabrics. Now a days laundry people needs faster results in less time & money hence chemical suppliers combined Neutral & acid cellulase in such way that it works faster & with better results than acid cellulase with cost effectiveness & known as Hybrid enzyme. Laccase is bio bleaching agent & alternative for conventional bleaching agents. This impart greyer cast to blue
