·         Processing involves conversion of grey cloth or loom state fabric into usable state

·         Grey cloth/loom state fabric-this is a fabric that comes from the loom or knitting machines and which is not suitable for immediate use or for dyeing

·         Such materials has impurities such as size, oil and dirt that is picked up during processing

 

Stages involved in processing

They include:

a)      Fabric preparation or preliminary processing

b)     Coloration –dyeing and printing

c)      Finishing

 

a)      FABRIC PREPARATION/PRELIMINARY PROCESSING

1)      Grey cloth inspection

This is done to detect fabric faults and the purpose of this inspection is to find, mend the defects and give feedbacks to the weaving and knitting department

 

       These faults include:

·         Reed marks-This is a warp way split in a woven fabric caused by a damaged or a defective reed

·         Broken picks-This is a weft that is inserted only in path of cloth width and is due to the weft breakage during the weft insertion

·         Missing picks-It’s a missing weft or incomplete sequence of weft during weft insertion in multi-shuttle

·         Slub –Are spinning short abnormally thick places in a yarn

·         Neps –this are spinning faults which appear as small knots of entangled fibers usually in cotton fibers

·         Knots –This is a mark where a weft or warp yarn gets entangled when weaving

·         Oil stains –this are stains connected from machine during weaving or knitting

 

2)      Singeing

The grey cloth has fibers projecting from the surface giving a hairy appearance. This projecting fiber are removed to get good results in dyeing or printing

Singeing is done by burning the hairy surfaces away

 

3)      Scouring /washing

It aims at uniform removal of waxes and fatty compounds or oil so that the material can be wetted out ready for dyeing

Scouring cotton

·         Scouring in cotton is referred to as Kiering, cotton fabric is treated with boiling alkali which is usually in large iron vessels known as Kiers

·         The alkali used is always sodium hydroxide, when the alkali meets with fats it forms a soap which splits the fatty compounds in a process known as saponification

·         The impurities are kept suspended in the detergent solution

·         During scouring process the Kier’s are enclosed so that cotton can be boiled under pressure in the alkaline solution to reduce the scouring time

            Scouring wool

·         This is done by moving the fabric through warm soap solution

·         It can also be done by use of Dolly scouring machine

·         A synthetic detergent or sodium carbonate is used  for this purpose

 

4)      Bleaching

It aims at whitening fabrics. We have bleaching that have reducing agents and oxidizing agents. Animal fibers are bleached with reducing agents while fibers are bleached with oxidizing agents

·         Examples of bleaching agents use include sodium peroxide, sodium chloride, Sulphur dioxide, Hydrogen peroxide and Sodium hypochlorite

 

5)      Mercerizing process

It’s a chemical process in cotton and linen fabrics aiming at increasing absorbency and improving affinity to dyes. The fabric is usually treated with alkalis which is usually sodium hydroxide solution which causes the fibers to swell.

The alkalis is then removed by washing in water then exposed to warm dilute acid rinsed again and then dried

 

6)      Desizing

This is the removal of excess size applied to yarns during weaving. The process entails breaking down the size so that it is soluble in water without damaging the fibers

This is done by steeping the fabric in dilute acid

7)      Caustic Reduction - the surface of the polyester fibers is eroded away in a caustic bath which reduces the weight of the fabrics and gives them a silk-like feel. 

 

 

FABRIC COLORATION

It is the application of color to the fabric. Dyeing and printing are the steps that impart color to a fabric, making finished products such as garments much more attractive. Dyeing and printing is highly complex, requiring years of study and / or experience. Only the highlights will be summarized here. 

Dyes and application methods vary greatly. Colorfastness is the degree to which a fabric will retain its color when subjected to adverse conditions such as sunlight, detergent, bleach, or other agents. Different types of dyes, and different methods of application produce substantially different levels of clarity and colorfastness. For optimal quality of the fabrics and final products, dye types and application methods must be carefully selected according to the fiber type, fabric type, and expected end use.  

Color can be imparted at any one of several stages in textile and garment production, from the fiber to the sewn garment. As with the types of dye and the application method used, the point at which the color is introduced affects the clarity and fastness of the color. 

 

Table 2. Stages at which color can be applied to a textile product.

 

Stage	Step
Fiber	The chemical solution used to make synthetic fibers may be dyed before being extruded into fibers.
Yarn	Yarn may be dyed to allow weavers or knitters to build colored patterns into the fabric itself, as in the case of woven stripes or plaids, ikat patterns, or knitted stripes or plaids.
Fabric	Fabric can be dyed a single color, or it can be printed with a colorful pattern using one or more of several different printing techniques.
Garment	Fully assembled garments can be dyed, though this is seldom done.

 

Fiber Each point at which color is imparted has its own advantage. Solution – dyed fiber generally enjoys very high colorfastness. Fiber dyeing is really only suitable for man – made fibers that can be dyed in solution form (before the actual fiber is formed) however, as attempts to dye loose fibers easily tangles and mats fibers into an unusable mess. 

Yarn. Yarn can be dyed after spinning.  Dyed yarn can be used to create woven stripes or plaid designs in fabric. However, dyeing at the yarn stage is relatively difficult, often resulting in uneven color application. At this stage, yarn can be dyed either in skein form (large bundles of loosely wrapped yarn) or wound on tubes or cones. The former allows yarn to move more freely in the dye bath or dye solution, helping ensure greater uniformity of dye penetration and therefore better color uniformity. It may also result, however, in tangled yarn. For dyeing on cones, yarns must be wound on special perforated tubes or cones that allow the dye solution to be force through the layers of yarn from the interior as well as the exterior. Dyeing cones of yarn requires high – pressure equipment that can force dye through hundreds of layers of yarn wrapped tightly around the cone, but this method generally produces fewer tangling problems. 

Whether dyed in skein or cone form, each batch of yarn dyed together is referred to a dyelot. While color should be uniform within a single dyelot, there is often a discernable difference in color between dyelots. For quality control is it vital to segregate dyelots so only one is used in a single garment, helping ensure that within the garment, yarn (hence fabric) color will be uniform. 

Fabric. Dyeing and / or printing fabric allows the greatest design flexibility but varying levels of colorfastness, depending upon the dyes and methods used. It also requires that substantial quantities of fabric be dyed or printed the same color or pattern to be cost effective. As with yarn dyeing, each batch of fabric dyed becomes an individual dyelot. With fabric, individual dyelots should also be segregated at the apparel manufacturing stage to help avoid color – related problems in the finished garment.

Modern technology and computers are allowing designers to print only select areas of a fabric, depending upon the shape of the garment to be made from the fabric, effectively eliminating a split in the printed pattern where fabric is seamed. To date, however, this remains more a laboratory experiment than a commercially viable printing method. (For greater detail on fabric dyeing and printing, see Fabric dyeing and printing section below.)

 

Garment. Last, fully - constructed garments can be garment - dyed, allowing retailers to wait until the last point in the manufacturing chain to make decisions on the number of garments to produce in each color, thereby reducing the risk of unsold inventory from bad color decisions. With garment dyeing, however, more highly specialized equipment is required, the entire garment must be dyed the same color, threads must accept dye in the same way as base fabric or off quality results, and it may be more difficult or impossible to do certain additional types of fabric processing normally done after dyeing or printing many apparel fabrics.

 

·         There are two methods used mainly dyeing and printing

1.      Dyeing

Different dyeing materials are used for different fiber materials. Various dyeing materials exist, as the fibers possess different reactive groups due to their chemical structure. These are available for the absorption of the dyeing material.

In the following specific dyeing materials are mentioned for some fiber materials

i.                    Cellulose:

-           Substantive/direct dyes

-          Diazotization dyes

-          Developing dyes

-          Vat dye

-          Reactive dyestuff

-          Sulfide dyes.

ii.                  Wool:

-          Acid dyes

-          Metallic complex dyes

-          Chrome developed dye.

iii.                Polyester:

-          Disperse dye.

A fabric can be dyed as a result of an affinity of the dyes for the fabric (adhesive powers = physical linkage) or via genuine chemical linkage of the dye with the fiber (with reactive, acid, and cationic dyes).

These mechanisms produce a very high color fastness. In the case of dispersion dyes a solution process takes place in which the dye molecules are dissolved in the textile fibrous material. The dyeing of fiber blends is difficult owing to the different affinities, the different dyeing material stabilities of individual dyes in the liquor, and so forth. In this case, both fibrous materials have to be dyed directly and evenly

In principle, the following coefficients have to be considered for the decision on which plant the material will be dyed:

·         Fiber raw material or raw material mix

·         Future field of application (authenticity)

·         Costs

·         Structure of the textile fabric

·         Feel of the fabric

·         Job size

·         Reproducibility, and so forth

Dyeing Methods

(a)  Batik Dyeing

●       Part of the fabric is coated with wax and dyed. Dye can only penetrate fabric area without wax. The waxed area is left blank. 

(b)  Dope Dyeing (Pigmentation)

●       Dope dyeing refers to the coloration of man-made fibers that takes place in polymer extrusion.

(c)  Cone and Beam Dyeing

●       Cone and beam dyeing are yarn dyeing.

(d)  Batch Dyeing

●       Batch dyeing refers to the process of dyeing fabrics in a batch of a few tens of yards to a few hundred yards. 

2.      Printing

Multicolor patterns can be manufactured either by a processing of dyed yarns or by printing textiles with dyes. Textile printing mills provide textile fabrics with colorful motifs, as well as tasteful and appealing scenography and pattern.

Special attention has to be paid on high color brilliance, exact and sharp outlines of the pattern, as well as a high degree of color fastness. In contrast to dyeing of textiles, in which the dye is absorbed evenly out of aqueous dye liquor owing to chemical and physical processes on the textile fiber material, textile printing is the locally limited staining (sampling) of the textile fabric. The pattern can result from one or more colors. The same chemical and physical processes that occur in dyeing also take place between the textile fiber material and the dye

Printing Methods

(a)  Direct Printing

●       A process of printing dyes directly on fabrics to create print patterns. This technique creates colored patterns on white fabrics.

(b)  Resist Printing

●       Resist printing refers to the application of a resisting agent such as wax or colorants to specific patterns to prevent the penetration of another dye.

(c)  Discharge Printing

●       The function of discharging agents is to remove colors from fabrics.

(d)  Transfer Printing

●           The printing is then transferred to textile fabrics through ironing. 

FINISHING

Mechanical and chemical treatments or finishes may be added to fabrics to enhance appearance and / or performance of the finished apparel product. Common treatments or finishes include physical treatments such as calendaring, napping, brushing, sanding, and chemical treatments such as permanent press, water repellant, and / or flame retardant finishes. Flame retardant finishes are required for certain types of clothing sold in the United States, such as children’s sleepwear. Examples of specialty finishes and their uses are listed in the table below.

Table 3. Textile finishes  

Finish	Temporary / permanent	Purpose	Example of use
Physical finishes
Calendaring	temporary	give shine	girls’ party dresses
Napping	semi-permanent	give softness, and “direction” to fabric	flannel shirts
Brushing	Semi-permanent	give softness, and “direction” to fabric	flannel shirts
Sanding	permanent	give distressed or worn appearance	faded jeans
Chemical finishes
Permanent press	Semi-permanent; wears off with repeated washing	prevent wrinkling, reduce need for ironing after laundry	men’s tailored (business) shirts
Water repellant	Semi-permanent; wears off with repeated washing	cause water to run off fabric surface	raincoats
Flame retardant	Semi-permanent; wears off with repeated washing	reduce speed at which fabric or garment will burn when exposed to an open flame such as a lighted match or burning cigarette	children’s sleepwear

 

 

(a)  Mechanical Treatments/Physical finishes

  i.      Calendaring – to produce high luster fabrics

Involves running fabric between heavy metal drums that turn at varying speeds. Heat and pressure are used to produce a smoothness and sheen on the surface of the fabric similar to that sometimes caused by ironing a piece of dark – colored cloth i.e. compression of the fabric between two heavy rolls to give a flattened, smooth appearance to the surface of a fabric. One drum may be engraved, thus imparting a pattern to the sheen, creating a subtle watermark – type effect on the surface of the fabric. The effect created by calendaring disappears with repeated laundering or dry cleaning

 

ii.      Embossing – to produce raised or projected figures or designs

 

iii.      Brushing (raising or napping) – A technique used to produce a brushed or napped appearance. Achieved by teasing out the individual fibers from the yarns so that they stand proud of the surface. To raise the fibers on the surface. Plucking the fibers from a woven or knitted fabric to give a nap effect on the surface.

By using wire brushes to scrape the surface of the fabric, raise fibers from the surface of the exposed yarns, and thereby creating a more matte appearance and softer feel to the fabric surface. If done too harshly, these treatments abrade the fabric weakening it and even wearing holes in the fabric. They nonetheless remain popular, particularly in such wearing apparel as men’s flannel shirts.

 

iv.      Sueding or emerising or sanding and peaching – This process involves the use sandpaper to abraid the surface of the fabric to produce a suede-like appearance. i.e. to produce a raised surface similar to suede on fabrics

 

v.      Cropping – This is a process by which the fibers which protrude from the surface of a fabric are cut at even height. Cutting the surface hairs from the fabric to give a smooth appearance, often used on woolen goods where the removal of surface hair by a singeing process is not possible

 

vi.      Shrinkage control (sanforizing process) – to preshrink cotton fabric

 

 

vii.      Pleating – to press pleats permanently

viii.      Felting – to compact masses of wool fiber

ix.      Decatizing - to stabilize wool fabrics.

x.      Eat setting – to stabilise thermoplastic (synthetic) fabrics 

xi.      Laser trimming – to produce shapes of hole on fabrics

(b)  Chemical Treatments

Chemical process may be described as those processes which involve the application of chemicals to the fabric. With the development of higher performance yarns, and the popularity of distressed looks in fashion apparel, and consumer concern about processing chemicals such as formaldehyde. The most common for wearing apparel are permanent press or no – wrinkle finished, water repellant finishes, and flame retardant finishes. Each serves a separate and distinct purpose for the consumer. 

  i.      Permanent press - finishes are most commonly used for fabrics destined for men’s dress shirts. These finishes help prevent wrinkling of cotton or cotton / polyester fabrics when laundered, thereby improving the appearance during wear, and reducing the ironing required after home laundry. Permanent press finishes have been popular with businessmen and their wives.

 

ii.       Water repellant finishes - These chemical treatments help prevent hydrophilic fabrics such as cotton or cotton blends repel water that touches the surface of the fabric. Such finishes are widely used for fabrics intended for raincoats and some other outerwear. Although they do not prevent water from soaking into the fabric in heavy rains or under prolonged exposure, they do help substantially. Similar finishes may be applied to help prevent soiling when fabric is exposed to dirt.

 

 

iii.      Flame retardant finishes - These finished are mandated by law for certain types of wearing apparel. Most notable, are the requirements for children’s sleepwear. Anyone considering manufacturing children’s sleepwear should take care to research the current legal requirements for flame retardant finishing.

 

iv.      Shrinkage resistance and Crease recovery/wrinkle free – cellulose molecules are cross-linked by resin, the resulting fabric from such a process would have an improved crease recovery. However, in addition to improving the crease recovery, it was also found that resin finishing improved the dimensional stability of the fabric washing

 

v.      Soil release (stain release) – the ability of a treated texture to shed soil during the washing process. One of the problems in the laundering of textiles is the ability of the fabric to be wetted by the cleaning solution. Ant treatments which encourage the wetting of the textile will act as soil release agents. (Easy care finishes)

 

vi.      Antistatic finishes – static electricity is formed when two dissimilar materials are rubbed together, it cannot be formed if the materials are identical. When this dissimilar materials are rubbed a separation of charges occurs and one of the materials becomes positively charged and the other negatively charged. Antistatic treatments are based on the principle of making the fiber conductive so that high charge densities are dissipated before sparks can form

 

vii.      Mothproofing finishes and insect damage – in the face of the widespread occurrence of keratin-eating pests, there is a very great need for the application of agents which would effectively stop destruction of fibers