Garment processing

Garment processingINTRODUCTIONThe concept of garment dyeing is not new. Even in good old days, the old garments used to be dyed by households or by commercial launderers, which was basically done for changing the color of the faded garments to have a newer look. Articles like towels, linens, napkins, table cloth, hosiery goods, etc, are being processed in the ready made form only since the last four decades. The garment dyeing of cotton garments such as trousers, jackets, shirts, skirts and tops is gaining popularity and is relatively new trend in the Indian garment industry. Garment dyeing has now become an important segment of apparel industry and its potential has yet to be exploited in India. Our society is gradually becoming more sensitive towards quick fashion changes, probably due to influence from the western countries. Therefore , it becomes necessary for garment suppliers and manufacturers to fulfill the customers demand by changing over to quick response system.What is Garment dyeing ?Garment dyeing may be defined as the application of color to fully fashioned apparel articles and these fashioned apparel articles may be in the form :-Garments cut and sewn from either prepared or unprepared knitted fabrics and then dyed.Garments and / or components knitted from either prepared or unprepared yarn then dyed.Garments manufactured from either prepared or unprepared woven fabric and then dyed. Mixed fabric garments, i.e., woven and knitted fabrics manufactured from prepared fabrics and then dyed. Out of four types of textile processing viz.- fibre processing, yarn processing, fabric processing and garment processing, the last option garment processing has gained momentum in past few years due to denim garments which is the largest garment segment being processed by this method. There are many advantages of wet processing of denims like it give various novel effects and various processes like bleaching could also be done at preferred parts of the garments and so on. There are mainly two sub-segments of garment processing:-

Garment wet processing The dyeing of the garments demands more care than fabrics due to the fact that the processing involves value added goods. The entire garment dyeing activities may be broken down into four categories, namely, fully fashioned garment dyeing, cut and sewn garment, dyeing of 100% cotton goods for boutique trades and processing of denims leading to stone wash, acid wash, washing and highlighting effects.

Wet processing machinesGarment dyeing machines and their principlesTypes of construction

Types of liquor and government movement

Paddling machine

Mechanical arrangementslike paddle, drum

2. Drum machine

Hydrodynamic movementwith adjustable jets

3. Washing-centrifuging machines

Hydrodynamic circulating dyeingmachines with so called floatingliquor circulation principle

4. Jet dyeing centrifuging machines

Jets and nozzles are used tofacilitate movement of thegarments

Paddling machineIt consist of either horizontal or vertical paddles .Paddles are widely accepted for sweaters, loosely knitted goods due to their soft dyeing action, which avoids abrading and pilling of the garments.For gentleness, the dyeing is carried out with m:l ratio of 30:1 to 40:1, the blades of the paddle are either curved or rounded and the rotating speed of the paddle can be regulated from 1.5 rpm to 40 rpm. Overhead paddle, lateral paddle and high temperature paddle machines serve the needs of the entire range of the garments.

Washing centrifuging machineThis machine with multi-pocket designs have compartments to control garment movements, abrasion due to mechanical action by carrying the garments through the dye liquor in the compartments. By making more compartments the tumbling effects and the entanglements in the garments are reduced and also are the abrasions associated with it.

Drum dyeing centrifuging typeIn drum type machines, a perforated drum is suspended lengthwise in a horizontal position, submerged in the dye liquor . The drums are divided into compartments and are capable rotating in both the directions at 2 rpm to 20 rpm, where temperature varies up to 140c. Drum dyeing centrifuging machines are also called multipurpose drum machines or multi-rapid dyeing-centrifuging machines, since these machines can perform scouring, dyeing, centrifuging and conditioning successively with automated controls.

Jet circulation machineIn jet machines, the dye liquor and goods are kept in circular motion by jet nozzles whose direction and force are adjustable. Turbulence nozzles at the bottom ensure liquor circulation, prevent goods from sinking and allow opening them. the machine capacity varies from 25 kg - 125 kg of dry weight with m:l ratio of 1:25 to 1:40 and temperatures as high as up to 130 C.

Garment Finishing :-through wet processing is responsible for adding beauty to the garment, proper finishing could provide better look to the garment, change the feel of the fabric and bring about a change to the fabric. Typical denim wet finish includes desizing to soften the fabric and stonewashing to remove color and add contrast to the fabric.

DESIZING:- Desizing is the process in which the size applied to the warp yarn before weaving is removed to facilitate the penetration of dyes and chemicals in the subsequent wet processing operation. The purpose of sizing is to form coating of sufficiently strong and woven fabric.

Types of Desizing:-Acid desizing In this method cotton fabric is treated with dilute sulphuric acid with a concentration of 5-10 gpl at temp of 40oc for 3-4 h. Dilute acid attacks the polymer chain of starch and due to chain cleavage of starch molecule short water soluble or dispersible chain segments are formed.Enzymatic desizing Enzymes have become extremely popular in the industry because they are easy to use and applicable in many process.

Enzymatic desizing carried out for denim garment by passing it through hot water and then padded with the desizing mixture containing 0.5-2% malt extract and Non-ionic wetting agent at 60-70c.

Wetting agents helps the enzyme to penetrate the size film.

ProcessConc(g/l)Phtemp0c Malt Diastase 3-204.5-5.550-60Pancreattic Diastase

1-36.8-7.550-60Bacterial Diastase0.5-16.5-7.560-70Desizing with amylases enzymatic desizing using amylase is the most popular method to remove starch and has been used in the textile industry for several decades. Alpha amylase break down the starch into water soluble sugars by cleaving internal 1,4 linkages. Although natural sizes of starch origin can easily be removed by alpha amylase, variable such as enzyme type and concentration, process, ph, temperature, time, mechanical action should be properly controlled to achieve the best desizing results. Advantages of enzymatic desizing over acid desizing:-Higher efficiency and specificity in actionNo fibre damageAvoiding the use of hazardous chemicalsAbility to use wide range of process conditions including processing at room temperature and complete biodegradbility of the effluent.Stone washing :- Stonewashing added new dimension to denim garments in the late 1970s; the process enabled artificial ageing of denim garments, which imparted a fashionably aged new look. As the name stonewashing implies, the blue jeans were washed with pumic stones to achieve a faded look.Process:-The jeans are washed with oval or round pumice stones which should all have roughly the same format. The pumice stones are very light with a rough surface. Normally after desizing, Stone wash process starts with pumice stone addition in rotary drum type garment washer, process time varies from 60-120mins.

Degree of colour fading depends on:- Stone ratio { stone weight to f/c weight (0.5 3:1)}Washing timeWeight of stones Load of garments (heavy denim, heavy stone)Sequence of stone washing :-Load the machine with garmentDesizing oxidative or enzymaticRinsingLoad machine with stonesRun machine for 30- 60 min depending on the abrasive effectRinsingTumble dryer

Disadvantages of stone washMachine damage Fabric may damageStone dustEffluent treatment

ENZYME WASH Limitations and drawbacks associated with stone washing process, can be overcome by using new enzyme based washing technology.Cellulase enzymes are natural proteins which are used in denim garment processing to get stone wash look on to the denim garments without using stones or by reducing the use of pumice stone.Cellulase attacks primarily on the surface of the cellulose fibre, leaving the interior of the fibre as it is,by removing the Indigo present in the surface of the fibre.

Denim bleaching: In this process, as a stone oxidative bleaching agent such as sodium hyprochlorite or KMNO4 is added during the washing with or without stone addition. This coloration is usually more apparent depending on the strength of the bleach liquor, quantity, temperature and treatment time.Sequence :-Load the machine.Desize (oxidative)RinseBleaching (hypochlorite)Rinse Antichlor treatment to remove residual chlorineRinse OBA / FBA optionalRinsingTumble dryer

LIMITATION:- Process is difficult to control i.e. difficult to reach the same level of bleaching in repeated runs. When desire level to bleaching reach the time span available to stop the bleaching is very narrow.Due to the harshness of chemical, it may case damage to the cellulose resulting in sever strength losses and / or breaks or pinhole at the seam, pocket, etc. Required antichlor treatment. Problem of yellowing is very frequent due to residual chlorine.

Biobleaching with laccase and mediator :- laccase is the newest enzyme class to be introduced into denim finishing.laccases are multi-copper oxidases that catalyze the oxidation of a wide range of phenols, including indigo, under simultaneous reduction of oxygen to water. Laccases alone are not effective in decolorizing indigo on denim and require a mediator, which mediates electron transfer from indigo to moleculer oxygen. Since the laccase and mediator only degrade indigo

Cont..without affecting the weft yarns, the resulting finish exhibits unique washdown of denim, with grey castGarment pigment dyeingPIGMENTS: These are the organic coloring compounds having no affinity for the fibres. Pigments have no chemical reaction with the substrate and require adhesive,resin or bonding agent for fixation on fabric. The main reason behind their usage is distressed washed out and faded look

Pigment dyeing :- It is refers to the application of pigments just like dyes by an exhaust method or pad application.

Generally pigments are either anionic or non-ionic in nature when disperse in water when applied on cellulose will not have affinity towards anionic cellulose in the dyebath.

So Ionic nature of the fibres are changed prior to the dyeing by different types of cationic pretreatments.

Types of pigments

Cationic polymers :are used that form a layer of cationic charges when applied to the fibre surfaces, eg: Polyacrylates, Polyimidazoles, Poluamino condensates.

Reactants: are the small molecules that modify the fibres by forming covalent bonds with the cellulosic fibres.These cationic pretreatments creates cationic charges on the fibre which causes anoinic materials(Pigments) to be strongly attracted to the fibre.

Efficiency of exhaustion is affected by process parameters such as:-Dosage-Optimum quantity is to be used,higher dosages reduces pigment build up ability and level dyeing ability.pH- Bath is to be maintained at slightly acidic side to achieve better exhaustion which gives uniform build up, desired shade depth.Temp- It is between RM temp to 80c which depends on polymer structure of cationizer.MLR- Too short MLR gives uneven build up of cationizer, generally 1:15 or 1:20 MLR is recommended.Time- Optimum time should be there which depends upon the machinery specification and agitation level

Advantages of Pigment Dyeing

Very short dye cycle time.

Good light fastness except fluorescent colours.

Novelty effects can be achieved by altering the chemicals dosage and change in processed.

4. Conventional equipments can be used.

5. Greater fibre selection flexibility

Garment dyeing pros and consProblems and remedial measures :- The dyeing of garment requires much more care than dyeing of the fabric, though there is very little difference in the dyeing procedure. This is mainly due to the fact that the value of the fashioned garment is much more than the fabric and unlike the fabric, it is in a twisted and folded form during the dyeing process. The majority of problems attributed to garment dyeing basically dpend on four main parameters:-The pre-treatment of the garment prior to dyeing.The quality and the type of the material used in the making of garment, viz, fabric construction, sewing thread, buttons, zippers, pocket linings, etcThe dyeing process.The machinery used for dyeing.Variation in shade or depth of shade within the garment panels or from garment to garment, dyed in the same lot :- This problem mainly occus due to the mixing of the panels cut from piecees of unmercerised, mercerised and causticised fabrics. The defect cannot be totally rectified even though by using selected dyes or using a single dye with minimum shading properties. In either cases, the unmercerised cotton will be to some extent lighter in shade and must be accepted. So it is necessary to identify and code the mercerised and unmercerised fabrics pieces prior to cutting and care should be taken during stitching to prevent mixing of panels.White undyed or light seams : This happens mainly due to tight stitching which further gets tighter due to the shrinkage during a higher temperature of dyeing, therby preventing dye penetration on the seams and underneath the stitches. In this case, the shrinkage properties of sewing thread should be taken into consideration for a particular method of dyeing and, accordingly, the stitching tension should be adjusted. Dullness and corrosion in metallic fastner in the garment during garment dyeing: Fashion garments ready for dyeing are usually fitted with metallic buttons, zippers, studs, etc. These items should be checked for their reaction with the dye system. Otherwise, chances are there that dye system to deteriorate the polished metal surface or cause galvanic corrosion and hamper the appearance of the garment. Therefore, metal zippers and buttons should be chemically resistant to the dye and dyeing process. Nickel plated brass zippers and buttons are less affected by the chloride ions from electrolyte and also give protection to the dyestuffs containing copper. polyester buttons and zippers either dyed or undyed can be used on 100% cotton garments to avoid all drawbacks of metallic fastener.Problem of deep dyed or lighter dyed polyester zippers and buttons than the body of garment: This problem mainly persists on fibre garments with nylon or polyester fastners. This problem be avoided by dyeing the zippers, buttons separately, prior to putting on the garment. In case of 100% cotton with undyed polyester zippers and buttons, past shades on the fastners can be achieved by adding low energy disperse dye with a direct dye bath. In case of reactive dyeing low energy disperse dye can be added at soaping stage. In order to get deeper shades carriers are added along eith disperse dyes.Puckering of seams during garment dyeing: A proper selection of swing thread is important, both from the point of view of garment manufcturing as well as dyeing. While stitching garments meant for dyeing, it is necessary to maintain the sewing tension at minimum level, so as to get slack stitches. This reduces the possibility of puckering due to shrinkage of thread during dyeing process.Advantages of garment dyeing :

Flexibility towards fast changing marketing trendsQuick response and rapid turn aroundFlexibility towards dye shades and finishesFlexibility of lot sizeFlexibility of items to be dyedComparatively less rejectionsLow inventory small capital investmentFancy effectsDisadvantages of garment dyeing :

Labour intensive process which requires a thorough piece by piece supervision at every stage of processingDefects related to yarn, fabric, sewing thread, interlining, etc.. Become visible after dyeing.Poor appearance in which dyed garment become hairy, fuzzy, beatenup, wrinkled if desired.Poor reproductibility of shades Special care of the dyeing properties as well as the effect of their presence on dyeing process is needed.More material handling, as compared to the pieces dyed goods, the extent of handling is more.

Quality control in garment processing The garments produced from woven fabrics have produced many problems, and experience has shown that existing styles as developed for piece-dyed fabric cannot be just assembled from grey fabric and thrown into the dyeing machines, unless they have been engineered from the original design stage for garment dyeing. The major areas for control are:-Seams, elasticated areas, waist bands, cuffs.Shrink behaviourChafe marks/creasesAccessoriesSewing threadInterliningsCare labelling depending on the fastness requirement.Thank you