Nonwoven Fabrics | Introduction and manufacturing process of nonwoven geotextile fabrics

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Nonwoven Fabrics 

Techniques by which fabrics are made directly from fibers, bypassing both spinning and weaving, have been used for centuries in the production of felt and bark cloth is called nonwoven fabric. It is also called nonwoven geotextile fabric because it is one kinds of geotextile. With the development of manufactured fibers, and, in particular, the synthesis of thermoplastic fibers, technologies have evolved that have made possible the large-scale production of non-woven fabrics. The first non-woven consumer product, an interlining fabric for the apparel industry, was introduced in 1952. Marketed extensively for both durable and disposable items, nonwoven fiber webs range from disposable diapers to blankets, from industrial filters to tea-bag covers. 

Nonwoven fabrics are textile structures “produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal or solvent means and combinations thereof” (ASTM 1998). This excludes fabrics that have been woven, knitted, or tufted. The Association of the Nonwovens Fabrics Industry (lNDA) in the United States and the European Disposables and Nonwovens Association (EDANA) help to further define what may be called a nonwoven fabric Oirsak and Wadsworth 1999). Over 50 percent of the weight of a non woven must be comprised of fibers with an aspect ratio (length to diameter ratio) of 300. This excludes paper products that are normally made of extremely short fibers. In additi”on nonwovens must have a density less than 0.4 grams per cubic centimeter, and felted fabrics are usually much heavier. 

American Fabrics (1974) magazine recommended that nonwoven fabrics be classified as durable products or disposable products. They defined a durable product as “one which is multi-use. It is not manufactured to be thrown away after a single application” (p. 40). Examples of this type of product are blankets, carpet backings, and furniture padding. Disposable products were defined as “made to be disposed of after a single or limited number of uses”. These are exemplified in disposable diapers, towels, or tea-bag covers. American Fabrics pointed out that some items are disposable not because of their durability but because of their purpose. Medical gowns, for example, or airplane and train headrests, might withstand multiple use, but for sanitary reasons they have limited use periods. 

Manufacture of nonwoven fabric

There are two steps involved in manufacturing nonwoven fabrics: 

(1) preparation of the fiber web and 

(2) bonding of the fibers in the web. 

A number of possibilities exist for each step, and in addition, the two stages may be distinct or can be carried out as a more or less continuous process. 

Fiber Web Formation Staple fiber webs are produced by either dry firming or wet firming. Dry-forming processes are carding, also called dry laying, and air laying. Carded webs are made in a manner similar to the process for felt webs and slivers for yarn spinning. Thicker webs can be built up by layering the carded webs. In air laying, the fibers are opened, suspended by air, and then collected on a moving screen. The wet laid process is similar to paper making in that a mixture of fibers in water is collected on a screen, drained, and then dried. 

Webs can also be made by the direct extrusion processes of spunbonding and melt blowing. Spunbonded fabrics are manufactured from synthetic filament fibers. Continuous filaments are formed by extrusion through spinnerets, and the filaments are blown onto a moving belt where they form a web. As the still hot and partially molten filaments touch, they bond. Polymers most often used are polypropylene and polyester. Spun bonded fabrics are strong because of the filament fibers and are not easily torn. They are used for a wide variety of products ranging from apparel interlinings, carpet backing, furniture and bedding to bagging and packing material. Spunbonded fabrics may be used in geotextiles to control erosion or in constructing roads. 

Some spun bonds made from olefins are used as a tough, especially durable substitute for paper in wall coverings, charts, maps, tags, and the like. Melt blowing also forms fabrics directly from fibers, but it differs from spun bonding in that molten fiber filaments are attenuated and broken into short lengths as they exit from the spinnerets. Cool air distributes the fibers onto a moving screen. 

As the fibers cool they bond, forming a white, opaque web of fine fibers. Because the fibers in melt-blown nonwovens are fine, the fabrics make good filter materials. Specialty products can also be made by layering spun bonded and melt blown fabrics or by entrapping absorbent fibers or other materials within the melt blown structure.

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Production of filament yarn with man-made fibre by Emulsion spinning and Wet spinning

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In melt spinning the fiber polymer is melted and the molten solution is forced through the spinneret. As the soft filaments emerge from the spinneret into the cooler environment, they harden into a standard filament form. Melt spinning requires no chemical change & any kind in the polymeric material from which the fiber is formed. It does require that the fiber polymer can be melted without altering the chemical state of the material. Fibers formed by this process are Nylon, Polyester, and glass. 

Emulsion Spinning 

Emulsion spinning is not used to a great extent but it is important for selected types of specialty fibers. Some raw polymeric materials cannot be processed by wet/dry/melt methods, because they either breaks drown when heated to a melting temperature or are not soluble in solution that can be used. For these substances the emulsion process is necessary. 

The polymer dispersed or emulsified into a solution, the dispersion or emulsion is then forced through a spinneret, and as the emulsion leaves the spinneret, the polymer form into a fibrous shape. Depending on the type & fiber, the fibrous form produced by this method may be staple / filament length. Teflon is an example of a fiber spun by the emulsion process. First, polymers, whether natural or synthetic, must be converted into liquid form to be spun. This is done either by dissolving the polymer in a suitable solvent or by melting it. This polymer solution or polymer melt is sometimes referred to as the spinning dope. Cellulose, the raw material for most naturally derived manufactured fibers, is not easily dissolved. Accordingly, the cellulose polymer is usually modified before it is dissolved. Synthetic polymers are put together in the plant before the dissolution or melting step. 

Before actually forming the fiber, certain characteristics can be added to the polymer material. Many manufactured fibers are naturally bright, with a high luster. If dull or semi-dull fibers are wanted, delustering agents can be added to the molten polymer to break up light rays and decrease shine. Colored pigments, flame retardants, and compounds to absorb ultraviolet light can also be added. Occasionally substances are added during polymer synthesis so that they are incorporated into the polymer molecules themselves. 

Wet Spinning 

Wet-spun polymers are, like dry-spun polymers, converted into liquid form by dissolving them in a suitable solvent. The polymer solution is extruded through a jet into a liquid bath. The bath causes coagulation and precipitation of the fiber. Solvents are usually recovered from the liquid bath and are recycled. Viscose rayon and some acrylics are wet spun. 

It is possible to add special chemical reagents to the liquid bath that produce selected changes in the fiber. This is done in the manufacture of some high-strength rayons, for example; into a liquid bath. The bath causes coagulation and precipitation of the fiber. Solvents are usually recovered from the liquid bath and are recycled. Viscose rayon and some acrylics are wet spun. The polymer or substance to be used is making the fiber is dissolved into some type & solution, then is forced through the spinning jet into another liquid, which react with fiber solution the process involves one & the following reaction: 

(a) The fiber polymer may have been chemically changed in order to make it soluble in the solvent used when this occurs the fiber solution reacts with the receiving solution & reverses the chemical reaction so that the material is reformed into a fiber shape. The difference is that in reforming, a filament fiber shape has been made rather than a polymer in some other form, such as fibrous mass, chip or pellet. This process refers to the fiber solution as a derivation & the fiber form, the solution into which this passes is the coagulating bath & the actual process is typically called regeneration. 

(b) Wet-spinning may also be used when the fiber solution does not change the chemical form of the fiber. The solution is forced into a coagulating bath, which reduce the concentration of the fiber solution sufficiently to reform the fiber, this time in a filament form Fibers formed by wet spinning are rayon, acrylicA variant of wet spinning, called dry-jet wet spinning, has been developed to produce some of the newer fibers such as the aramid. Instead of the spinneret being immersed in the spinning bath, it is placed slightly above the bath so that there is a small air gap, usually less than an inch. The fibers exiting the spinneret can be stretched to orient the molecules before they enter the bath to be solidified. 

This process develops high orientation and crystallinity in one step, rather than drawing in a separate step Although melt-, dry-, and wet-spinning techniques are used to form the vast major-ity of manufactured fibers, several other spinning techniques also exist and may be applied in a limited number of specialized situations. High-molecular-weight poly-mers, such as those in Spectra@ polyethylene, are formed by solution spinning or gel spinning. As in wet and dry spinning, the polymer is dissolved in a solvent. The polymer and solvent together form a viscous gel that can be processed on conventional melt-spinning equipment to form a gel-like fiber strand. Later in the processing, the solvent is extracted and the fibers stretched. Fibers made from polymers that have extremely high melting points and are in-soluble present obvious difficulties in spinning. Such materials may be spun by a complex process called emulsion spinning in which small, fibrous polymers are formed into an emulsion, aligned by passing the emulsion through a capillary, then fused or sintered (combined by treating with heat without melting), passed through the spin-neret into a coagulating bath, and subsequently stretched

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Production of filament yarn with man-made fibre by Melt spinning and dry spinning

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Man Made Fiber Formation 

Man-made fibers are polymeric forms that are produced by some type of chemical which or by the regeneration & natural polymers in a new physical form. The polymer is connected into some type & liquid / fluid state and forced through a spinnerette. Although most spinnerette are made with round openings, some may use orifices & other shape is order to produce fiber with special characteristics. 

The basic steps in producing manufactured fibers are as; 

The liquid polymer is then extruded through a spinneret. Each spinneret has a number of holes, and each hole produces one filament. As they exit the spinneret the filament fibers are solidified by cooling of melted polymers, by evaporating the solvent, or by precipitating the polymer from solution. These methods of solidification are the bases of the three primary fiber manufacturing processes. Other spinning methods that have been developed are described later in this chapter. 

Filament yarns are described by denier (that is, size) and number of filaments; for example, filaments described as 70/34 represent 70 denier/34 filaments. When fibers being extruded are intended for conversion into staple lengths, spinnerets with larger numbers of holes are used to produce more filaments that are later cut into staple lengths. Spinneret holes are spaced to allow the filaments to be extruded without touching each other. The holes must be exactly the same size to produce uniform fibers. The metal used in the plate must be capable of withstanding high pressures or corrosive spinning solutions. 

Most fiber spinning processes include a final step of drawing in which the filaments are stretched around rollers. 

Melt Spinning 

Melt spinning take advantage of the thermoplastic characteristics of polymers. Chips of solid polymer about the size of rice grains are dropped from a hopper into a melter where heat converts the solid polymer into a viscous liquid. The liquid forms a “melt pool” that is pumped through filters to remove any impurities that, would clog the spinneret and is delivered to the spinneret at a carefully controlled rate of Row. Melt spinning is simpler and cheaper than other spinning methods; therefore, it is used except when polymers cannot be melt spun. 

The spinneret holes are usually round, but noncircular holes are also used to make filaments of various cross-sectional shapes. Melt-spun fibers may be made through Y-shaped holes that yield a three-lobed fiber or C-shaped holes to produce a hollow filament, for example; The diameter of the fiber is determined by the rate’ at which the polymer is supplied to the hole in the spinneret and the windup speed, not by the diameter of the hole. When the molten polymer emerges from the spinneret hole, a cool air current is passed over the fiber, causing it to harden. Failure to maintain constant feeding speed of molten polymer or changes in the temperature of cooling will cause irregularities in the diameter of the fiber. Nylon and polyester are the most common melt-spun fibers. One of the latest developments in melt spinning has been the significant increase in spinning speeds. Processing speed has increased from less than 1,000 meters per minute in the 1960s to over 7,000 meters per minute today. This is the equivalent of a car traveling over 250 miles per hour. Higher-speed spinning is cost-effective and up to a certain point increases the orientation of the polymers in the fibers. Beyond a speed of about 6500 meters per minute, however, this advantage disappears as there is not enough time for the polymers to crystallize and the fibers may break. 

Dry Spinning 

In dry spinning the fiber solution is forced through the spinneret into a warm air chamber. The warm air causes the solvent used to make the fiber solution evaporate & the filament fibers are formed & hardened. This process, too may involve converting the fiber polymer into a different chemical form that is soluble in a suitable liquid As the solvent evaporate, the fiber polymer is reconstituted & return to its original chemical form, but now it is in a filament shape. 

Many polymers are adversely affected by heat at or close to their melting temperatures. Polymers that cannot be melt spun undergo other methods of spinning, such as dry spinning, to produce filaments. Dry spinning requires the dissolving of the polymer in a solvent to convert it into liquid form. Substances used as solvents are chosen not only because they will dissolve the polymer but also because they are safe and can be reclaimed and reused. 

The polymer and solvent are extruded through a spinneret into a circulating current of hot gas that evaporates the solvent from the polymer and causes the filament to harden. The solvent is removed and recycled to be used again. Dry-spun filaments generally have an irregular cross section. Because the solvent evaporates first from the outside of the fiber, a hard surface skin of solid polymer forms. As the solvent evaporates from the inner part of the fiber, this skin “collapses” or folds to produce an irregular shape. If the rate of evaporation is slowed, the cross section of the filament will be more nearly round. Acetate fibers and some acrylic fibers are dry spun. 

 

Fibers formed are: acetate, triacetate, acrylic, modacrylic, aramid fibers. 

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HOLLOW FIBERS | BI-COMPONENT FIBERS

HOLLOW FIBERS 

Hollow fibers are made of a sheath of fiber material and one or more hollow spaces at the center. These hollows may be formed in a number of different ways. The fiber may be made with a core of one material and a sheath of another, and then the central material is dissolved out. Alternatively, an inert gas may be added to the solution from which the fiber is formed, with the gas bubbles creating a hollow area in the fiber. Other experimental or proprietary techniques have been used to make hollow fibers. One involves spinneret holes with solid cores around which the polymer flows. 

Hollow fibers provide greater bulk with less weight. They are therefore, often used to make insulated clothing. For absorbent fibers such as rayon, hollow fibers provide increased absorbency. Some have been put to such specialized uses as filters or as carriers for carbon particles in safety clothing for persons who come into contact with toxic fumes. The carbon serves to absorb the fumes Bi-component Fibers 

As the technology for producing manufactured fibers has become more highly developed, manufacturers have turned to increasingly sophisticated techniques for creating new fibers. Not only are new generic fibers being created but also different polymers or variants of the same polymer can be combined into a single fiber to take advantage of the special characteristics of each polymer. Such fibers are known as bi-component fibers. 

The American Society for Testing and Materials (ASTM) defines a bi-component fiber as “a fiber consisting of two polymers which are chemically different, physically different, or both. Bicomponent fibers can be made from two variants of the same generic fiber (for example, two types of nylon, two types of acrylic) or from two generically different fibers (for example, nylon and polyester or nylon and spandex). The latter are called bi-component bi-generic fibers. 

Components in bi-component fibers may be arranged either side by side or as a sheath core. In making a side-by-side bicomponent fiber, the process requires that the different polymers be fed to the spinneret together so that they exit from the spinneret opening, side by side. Sheath-core bi-component fibers require that one component be completely surrounded by the other, so that the polymer is generally fed into the spinneret as shown in Figure. Variation in the shape of the orifice that contains the inner core can produce fibers with different behavioral characteristics. 

BI-COMPONENT FIBERS 

As the technology for producing manufactured fibers has become more highly developed, manufacturers have turned to increasingly sophisticated techniques for creating new fibers. Not only are new generic fibers being created but also different polymers or variants of the same polymer can be combined into a single fiber to take advantage of the special characteristics of each polymer. Such fibers are known as bi-component fibers. The American Society for Testing and Materials (ASTM) defines a bi-component fiber as “a fiber consisting of two polymers which are chemically different, physically different, or both. Bi-component fibers can be made from two variants of the same generic fiber (for example, two types of nylon, two types of acrylic) or from two generically different fibers (for example, nylon and polyester or nylon and spandex). The latter are called bi-component bi-generic fibers. 

Bi-component fibre

Components in bi-component fibers may be arranged either side by side or as a sheath core. In making a side-by-side bi-component fiber, the process requires that the different polymers be fed to the spinneret together so that they exit from the spinneret opening, side by side. Sheath-core bi-component fibers require that one component be completely surrounded by the other, so that the polymer is generally fed into the spinneret as shown in Figure. Variation in the shape of the orifice that contains the inner core can produce fibers with different behavioral characteristics.

POLYMER SPINNING | DRAWING OR STRETCHING AND HEAT SETTING OF POLYMER YARNS

POLYMER SPINNING 

Polymer spinning is important part of man made fiber and yarn manufacturing technology. Polymer spinning is very popular and result oriented synthetic spinning method. Although melt- spinning, dry-spinning, and wet-spinning techniques are used to form the vast majority of manufactured polymer fibers, several other spinning techniques also exist and may be applied in a limited number of specialized situations. High-molecular-weight polymers, such as those in Spectra@ polyethylene, are formed by solution spinning or gel spinning. As in wet and dry spinning, the polymer is dissolved in a solvent. The polymer and solvent together form a viscous gel that can be processed on conventional melt-spinning equipment to form a gel-like fiber strand. 

Later in the processing, the solvent is extracted and the fibers stretched. Fibers made from polymers that have extremely high melting points and are insoluble present obvious difficulties in spinning. Such materials may be spun by a complex process called emulsion spinning in which small, fibrous polymers are formed into an emulsion, aligned by passing the emulsion through a capillary, then fused or sintered (combined by treating with heat without melting), passed through the spinneret into a coagulating bath, and subsequently stretched. 

DRAWING OR STRETCHING OF POLYMER YARN

Both crystalline and amorphous arrangements of molecules exist within newly formed filaments. It is possible to orient these molecules to make them more parallel to the walls of the filament, and therefore more crystalline and stronger, by stretching the filament before it is completely hardened after polymer spinning. 

Newly formed filaments are, therefore, subjected to drawing or stretching. Depending on the fiber type, this may be done under cold or hot temperature conditions and has the additional effect of making the filament both narrower and longer. Fibers made from polymers that have a low glass transition temperature, such as nylon, can be drawn at room temperature. 

In case of polymer spinning, The polymers are mobile and can be pulled into positions parallel to the fiber length. Polyester, on the other hand, has a higher glass transition temperature and so must be heated to be drawn. Drawing is accomplished by stretching the fibers between two rollers, called Codet rolls, with the second roller rotating faster. 

Not all yarns are drawn to the maximum amount possible, because when a fiber reaches its maximum length, the extensibility of the yarn and fiber are lowered. Yarns that have not been fully drawn are called partially oriented yarns (POY). Those that have been fully drawn are called fully oriented yarns (FOY). Lower speeds in melt spinning produce fibers with lower orientation. As is true of many other textile processes, precise control of the process must be maintained so that the manufacturer can achieve the qualities needed in the final product. 

Other steps may be added, such as texturing (in which crimp is added to the filaments) or heat-setting treatments to ensure very low shrinkage as is required in fibers for automobile tires. Sometimes two or more steps may be combined into consecutive operations to reduce manufacturing costs, so that the fibers may go from spinning directly to drawing or from spinning to drawing to texturing. 

HEAT SETTING AFTER POLYMER SPINNING

Thermoplastic manufactured fibers may shrink when exposed to heat. To prevent shrinkage, such fibers are treated with heat during manufacturing to “set” them into permanent shape. Exposure during use and care to temperatures greater than the heat-setting temperature will counteract the heat setting, resulting in fiber shrinkage or loss of heat-set pleats or creases. 

As the technology for producing manufactured fibers has become more highly developed, manufacturers have turned to increasingly sophisticated techniques for creating new fibers. Different fiber shapes and sizes, as well as unique combinations of polymer types in the same fiber, are but several examples of these techniques. 

Fibre Blends; Properties of fiber Blended Yarns

Fibre Blends 

Fibre Blending is the process of mixing fibers together. As noted earlier, it can take place at any of several points during the preparation of a yarn. The purposes of blending are (1) the thorough intermixing of fibers and/or (2) combining fibers with different properties to produce yarns with characteristics that cannot be obtained by using one type of fiber alone. Self blending of bales of the same fiber is done routinely in processing natural fibers because the fibers may vary from bale to bale. In this type of blending, the mixing of as many bales as possible is done early in the processes preparatory to spinning so that the subsequent steps can help to mix the fiber still more completely. For the same reasons, even when two or more different fiber types are combined, blending is done as early as possible. Carding helps to break up fiber clusters and intermix fibers more thoroughly. However, if the fibers being blended require different techniques for opening, cleaning, and carding, as with polyester and cotton, then slivers can be blended. For blended yarns of different fibers, the blend level is the percentage by weight of each fiber. Blending is not limited to staple-length fibers. Filament fibers of different generic types can be combined into a single yarn. This can be done either by extruding these fibers side by side, during drawing, or during texturing. As described earlier, a blended yarn can be core spun with one fiber at the center and a different fiber as the covering or be wrapped with one fiber making up the central section and another the wrapping yarn. As yarn spinning and texturing technologies grow more sophisticated, we expand the possibilities of combining several different fibers into one yarn. Multiple-input texturing machines can produce specialty yarn blends. 

It should be noted that fabrics woven from two or more yarns each made of different fibers are not considered blends. These fabrics are, instead called combination fabrics. They do not behave in the same way as those fabrics in which, the fibers are more intimately blended and may require special care procedures. Regrettably, the Textile Fibers Products Identification Act (TFPIA) labeling requirements do not distinguish between blended fabrics and combination fabrics when fiber percentage contents of fabrics are given. 

Properties of Blended Yarns 

Fibers with different characteristics, blended into a yarn, can each contribute desirable properties to the final textile material. The ultimate performance is an average of the properties of the component fibers. For example, a fabric of 50 percent cotton and 50 percent polyester would have an absorbency intermediate between that of cotton or polyester. In some cases, however, the observed fabric property is not determined simply by the relative amounts of each fiber in the blend. In blends of nylon with cotton, the tenacity of the blended yarn initially decreases with increasing amounts of nylon because of differences in the breaking elongation of the two fibers. At the breaking elongation of the cotton fibers, the nylon fibers are not assuming their share of the stress, leaving the cotton to bear the load. 

The stage at which blending occurs also affects the properties of the fabrics. In general, the more intimate the mixing of fibers in the blends, the better the resulting properties. Yarns blended at the fiber stage exhibit a more effective averaging of properties than ply-blended yarns. Even though considerable study and evaluation have been made of optimum fiber proportions required to achieve desired results in blends, no certain conclusions have been reached. It is clear that extremely small proportions of fibers have no appreciable influence on performance, although they may have some effect on appearance.

Modern spinning method; Ultra Modern method of manufacturing yarn.

OTHER METHODS OF MANUFACTURING YARNS 

In addition to ring and open-end spinning, techniques that insert true twist into yarn, there are other types of yarn construction. Three of those that have some current commercial application are described in the following sections: false-twist, or self-twist, spinning; yarn wrapping; and splitting or slitting films made from synthetic polymers. The viability of these processes for commercial purposes varies. 

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Air-Jet Spinning 

Air Jet spinning is a ultra modern spinning or yarn manufacturing method The Murata Company, a Japanese firm, has commercialized an air-jet spinning machine that functions as follows. A largely untwisted sliver is fed into the machine. Two nozzles, each forcing an air jet against the sliver from opposite directions, cause fibers from the outer layer of the sliver to wrap around the interior fibers, thereby forming the yarn. 

Hollow Spindle Spinning 

Hollow spindle spinning is another modern yarn manufacturing process. In hollow spindle spinning, a sliver of core fibers is fed through a hollow spindle where it is wrapped by a filament yarn unwinding from the spindle. An interesting application of the technique has been in the manufacture of towels and other fabrics, in which the wrapped yarns are used in the pile. In this instance, the wrapping yarn is made from soluble polyvinyl alcohol (PVA) fibers. After the fabric has been put through the finishing processes, these yarns dissolve, leaving a soft, all-cotton twist less and absorbent yarn in the pile 

Core Spinning 

Core spinning is also a special spinning for yarn manufacturing. Core-spun yarns are usually made with a continuous filament core surrounded by twisted fibers or other yarns. Recently, core spun yarns with a staple core of one fiber and an outer sheath of another fiber have been produced by an adaptation of ring spinning. Two rovings, one of polyester and one of cotton, are fed through drafting rollers and then pass through separate channels before being wound on the spindle. The channel for the cotton sheath is longer, ensuring that it will wrap around the polyester core as the twist is inserted. Fabrics from staple core yarns are more durable and have more easy-care features than those of 100 percent cotton yarns. 

Making Yarns from Films 

Recently, various new techniques have emerged that allow yarns to be formed directly from synthetic polymers without the formation of fibers or the twisting of fibers into yarns. These processes include the formation of yarns by the split-film and slit-film processes. Slit-film yarns could be classified as monofilaments. Yarns made by the split-film process do not fit neatly into the categories of staple or filament yarns. 

Split Films 

In the creation of yarns by the split-film technique, a sheet of polymer is formed. The formed sheet is drawn in the lengthwise direction. Through drawing, the molecules in the polymer are oriented in the direction of the draw, causing the film to be strengthened in the lengthwise direction and weakened in the crosswise direction. This causes a breakdown of the film into a mass of interconnected fibers, most of which are aligned in the direction of the drawing, but some of which also connect in the crosswise direction. The process is known as fibrillation. 

The fibrillated materials can be twisted into strings or twines or other coarse, yarn like materials. The usefulness of split-film yarns is limited because the yarns created are coarse. Olefins are made into split-film yarns for use in making bags, sacks, ropes, and other industrial products. 

Slit Films 

Slit films are made by cutting film into narrow, ribbon like sections. Depending upon the process used for cutting and drawing the film, the tapes may display some degree of fibrillation, like that described for split films. When tapes are made that do not fibrillate, they are flatter and are more suitable for certain uses. Flat tapes are used as warp yarns in weaving and can be made into carpet backings that will be very stable, remaining flat and even. All types of tape yarns are used in making wall coverings, packaging materials, carpet backing, and as a replacement for jute in bags and sacks. 

Lurex@, a flat, ribbon like yarn with a metallic appearance, is a slit film yarn that is often used to add decorative touches to apparel or-household textiles. Lurex@ is made from single or multiple layers of polyester film. Multi-layered types are made by placing a layer of aluminum foil between two layers of polyester film. 

Monoply types are cut from metallized polyester film, protected by a clear or colored resin coating. The natural color of Lurex@ is silver. Other colors are produced by adding pigments to the lacquer coating or to the bonding adhesive. The width of these yarns ranges from 0.069 to 0.010 inch. 

Ply Yarns 

Ply yarns are made from two or more single yarns that are twisted together. Ply yarns are much more expensive than single yarns but are nevertheless often produced to achieve certain benefits. Ply yarns made from identical single yarns are more regular in diameter and are stronger. Ply yarns are often made to achieve particular decorative effects. 

In general, the steps involved in creating ply yarns include: 

1. Winding single yarns and clearing any flaws. 

2. Placing the required number of component yarns alongside each other, in place, ready for supplying to the machine 

3. Insertion of twist to form the ply yarn by any of a number of different machines 

4. Winding the finished yarn on a cone or package for delivery to the customer 

A number of different machines are used in making ply yarns, which may also be referred to as folded yarns. Ring-folding machines, for example, operate on the same principle as ringspinning machines except that instead of a roving being fed to the traveler, the single yarns to be combined are both fed together for twisting.

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Yarn construction; Basic yarn manufacturing process

YARN CONSTRUCTION 

Basic Yarn Manufacturing Processes:
Carding –– Combing –– drafting –– twisting –– winding. 

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As the fibers pass through these processes, they are successively formed into: lap, sliver, roving and finally yarn.
The manufacturing operation in which these stages occurred
(1)Lap to card sliver by the lading process
(2)Card Sliver to Cone sliver by combing process.
(3)Shiver to roving by the drafting, or drawing out process
(4)Roving to yarn by further drafting and twisting process.
(5)Yarn reeled on bobbins, spools or cones by the winding process. 

(1) Bending, Ending, Opening and Cleaning: 
(i) The cotton arrives at the mill in large bales weighing about 500 pounds / 225 kg. The compressed mass of raw fibers must be removed from the bales, blended, opened & cleaned.
(ii) Opening is necessary in order to loosen hard lumps of fibers & disentangle them.
(iii) Cleaning is required to remove trash – such as dirt, leaves, burrs, seeds, etc.
(iv) Blending is necessary to obtain uniformity of fiber quality.
(v) Blending: Mechanical bale pickers pluck thin, even layers of the matted fiber from each of a predetermined number of bales in turn and deposit them on Hooper. The fiber is mixed & passed to an opener.
(vi) Opening: As the mass of fiber passes through the openers, cylinders with protruding fingers open up the lumps & free the trash. The number & kind of cylinder, or beaters, employed depend upon the type of cotton that is being processed.
(vii) Cleaning: As the cotton is opened, trash falls through a series of grid bars. When the cotton emerges from the opener, it still contains small tuffs with about 2/3rd of trash.
(vii) This may be conveyed as a lap, which is loosely entangled mass about 1" thick and about 40" wide. Or it may be fed by chute directly to the card for further cleaning and fiber separation.

Blending

Opening and Cleaning

(2) Carding: 

(i) This is the process of arranging the fibers in a parallel fashion. This is necessary for all staple fibers; otherwise, it would be impossible to produce fine yarns from what is originally a tangled mass.
(ii) Before the raw stock can be made into yarn, the remaining impurities must be removed, the fibers must be disentangled, and they must be straightened.
(iii) The lap is passed through a beater section and drawn on a rapidly revolving cylinder covered with very fine hooks or wire brushes.
(iv) A moving belt of wire brushes slowly moves concentrically above this cylinder. As the cylinder rotate, the cotton is pulled by the cylinder through the small gap under the brushes, the teasing action remove the remaining trash, disentangles the fibers and arranges them in a relatively parallel manner in the form of a thin web.
(v) This web is drawn through a funnel – Shaped device that molds it into a round ropelike mass called the card sliver (about thickness of a broom stick).

Carding

(3) Combing: 
(i) In this operation, fine-toothed combs continue straightening the fibers until they are arranged with such high degree of parallelism that the short fibers called ‘noils’ are combed out and completely separated.
(ii) This procedure is not done when processing man-made staple fibers because they are cut into predetermined uniform length.
(iii) This operation eliminate, as much as 25% of the original card sliver, thus almost one-fourth of the raw cotton becomes waste.
(iv) The combing process forms a comb sliver made of the longest fibers, which, in then, produces a smoother & more even yarn. 

Combing

(4) Drafting / Drawing 

(i) The draw frame has several pairs of rollers, each advance set of which revolves at a progressively faster speed.
(ii) This action pulls the staple lengthwise over each other, thereby producing longer & thinner slivers.
(iii) After several stages of drawing out, the condensed sliver is taken to the slubber, where rollers similar to those in the drawing frame draw out the cotton further.
(iv) The slubbing is passed to the spindles, where it is given its first twist & is then wound on bobbins.

Drawing

(5) Roving: 
(i) Roving is the final product of several drawing out-operation.
(ii) These bobbins are placed on the roving frame, where further drawing out and twisting take place until the cotton stock is about the diameter of a pencil lead
(iii) To this point, only enough twist has been given the stock to hold the fibers together.
(iv) Roving has no tensile strength, it will break apart easily with any slight pull. 

Roving

(6) Spinning: 
(i) The ring spinning frame complete the manufacture of yarn
• By drawing out the roving
• By inserting twist
• By winding the yarn on bobbins.
(ii) Ring Spinning draws; twist s& winds in one continuous process. The traveler carries the yarn as it slides around the ring, thus inserting the twist.

Ring Spinning

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Ring Spinning 

The ring spinning could be defined, the process of manufacturing yarn with flying ring.

The ring spinner is made up of the following parts: 

Ring spinning 

1. Spools on which the roving is wound 

2. A series of drafting rollers through which the roving passes 

3. A guiding ring or eyelet 

4. A stationary ring around the spindle 

5. A traveler-a small, V-shaped clip on the ring 

6. A spindle 

7. A bobbin 

The roving is fed from the spool through the drafting rollers. The rollers elongate the roving, which passes through the eyelet, moving down and through the traveler. The traveler moves freely around the stationary ring. The spindle turns the bobbin at a constant speed. This turning of the bobbin and the movement of the traveler impart the twist to the yarn. The yarn is twisted and wound onto a bobbin in one operation. 

Bobbins must be removed from the machine when full. From here, bobbins are transported to a winding machine where yarn is wound onto packages. Automated systems for doffing and winding have been developed and are widely used. Winding is considered an important step. It provides an opportunity to condition yarn that is, to bring the yarn into equilibrium with the moisture in the atmosphere, and to add wax or other coatings that will facilitate weaving. Winding also allows the identification of flaws in the yarn and formation of larger yarn packages than the spindles on the ring spinning frame. 

1. The value and character of a yarn are determined by 

• Kind and quality of fibers 

• Amount of processing necessary to produce fineness. 

• Amount of twist, which increases tensile strength in the finished yarn. 

2. The purpose of the yarn must be anticipated, as this determines the number and kind & many manufacturing operations. 

3. The formation of yarn from staple fibers by shinning becomes possible when they have surfaces capable of cohesiveness. This quality is exemplified by the natural twist of the cotton fibers, which enables them to entwine around each other, the roughness of the linen fibers, which cause them to cling together, and the scale on the surface of the wool fibers, which cause them to graph each other. 

4. Flexibility permits the fibers to be twisted around one another. 

5. Uniformity & staple give yarn a required evenness & improve the quality. 

Yarn Twist due to ring spinning:

The amount of twist is an important factor in finished consumers’ goods. It determines the appearance as well as the durability and serviceability of a fabric. Fine yarns require more twist than coarse yarns. Warp yarns, which are used for the lengthwise threads in woven fabrics, are given more twist than are filling yarns, which are used for the crosswise threads. To retain the twist in the yarns and prevent any tendency to untwist or kink, the yarns are given a twist-setting finish with heat or moisture, depending upon the kind of fiber used. The direction of twist may be observed by holding the yarn in a vertical position. If the spirals conform to the direction of the slope of the central part of the letter S, the yarn has an S twist; if they conform to the slope of the letter Z, the yarn has a Z twist. 

Yarn Count maintain with ring spinning:

In the spinning process, there is always a fixed relation between the weight of the original quantity of fiber and the length of the yarn produced from that amount of raw material. 

This relation indicates the thickness of the yarn. It is determined by the extent of the drawing process and is designated by numbers, which are called the yarn count. 

The International Organization for Standardization (ISO) fixed relationship between the weight and length of all yarns: one tex equals 1 gram (g) per kilometer. The greater the weight, the thicker the yarn, and consequently the higher the tex number Because of the speed limitations in ring spinning, researchers concentrated on developing techniques for inserting twist into yarns that would permit more rapid production. A result of this search was the introduction, in the 1960s, of the open-end spinning machine, which operated at higher speeds but produced a yarn with slightly different characteristics than conventional ring-spun yarns with ring spinning.

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Rotor spinning; Open-End Spinning

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Self twist spinning or Open-End Spinning 

Open-end spinning omits the step of forming the roving. Instead, a sliver of textile fibers is fed into the spinning machine spinner by a stream of air. The sliver is delivered to a rotary beater that separates the fibers into a thin stream. It is carried into the rotor by a current of air through a duct and is deposited in a V-shaped groove along the outer edge of the rotor. Twist is provided by the turning of the rotor. 

Fibers fed to the rotor are incorporated into the rapidly rotating “open end” of a previously formed yarn that extends out of the delivery tube; hence, the name open- end spinning. As the fibers join the yarn, which is constantly being pulled out of the delivery rube, twist from the movement of the rotor is conveyed to the fibers. A constant stream of new fibers enters the rotor, is distributed in the groove, and is removed at the end of the formed yarn, becoming part of the yarn itself. 

The fineness of the yarn is determined by the rate at which it is drawn out of the rotor relative to the rate at which fibers are being fed into the rotor. In other words, if fewer fibers are being fed in while fibers are being withdrawn rapidly, a thinner yarn will result, and vice versa. The twist is determined by the ratio of the rotor turning speed to the linear or withdrawal speed of the yarn (that is, the higher the speed of the rotor, the greater the twist). 

Theoretically, a variety of different means may be used to form the yarn and insert twist. These have been divided into the following categories: mechanical spinning (of which rotor spinning is an example), electrostatic spinning, fluid spinning, air spinning, and friction spinning. Of these, only rotor and friction open-end spinning machines have been commercialized and most of the open-end spinning machines now in use are of the mechanical rotor spinning type Friction open-end spinning machines are also available. 

Friction spinning systems use friction to insert twist. A mixture of air and fibers is fed to the surface of a moving, perforated drum. Suction holds the fibers against the surface while a second drum rotates in the opposite direction. Twist is inserted and the yarn begins forming as the fibers pass between the two drums. The newly forming yarn is added to the open end of an already formed yarn, and the completed yarn is continuously drawn away. 

The advantages of open-end spinning are that it increases the speed of production, eliminates the step of drawing out the roving before spinning, and permits finished yarns to be wound on any sized bobbin or spool. As a result, it is less expensive. It produces yarns of more even diameter than does ring spinning. Yarns are more uniform in diameter, bulkier, rougher, more absorbent, and less variable in strength than are ring-spun yarns. 

Fabrics made from open-end spun yarns compared with ring spun yarns are more uniform and more opaque in appearance, lower in strength, less likely to pill, and inferior in crease recovery. A number of sources indicated that they are more subject to abrasion. 

Neither friction nor rotor spinning will produce yarns as fine and strong as ring- spun yarns, although recent advances have extended the range of yarn sizes possible. Open-end spun yarns have a handle that has been characterized as “harsh.” Some of the kinds of products that seem to be especially well suited to the use of open-end spun yarns are in filling yarns for fabrics where yarn strength is not a factor, toweling pile yarns, denim, and heavier weights of bed sheeting. The yarns even surface makes them desirable as base fabrics for plastic-coated materials. On the other hand, the more acceptable feel of ring-spun yarns has led knitwear manufacturers to prefer them, and they are better for fine blends of polyester and cotton.

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PRINTING METHDOS AND PROCESS MODIFICATIONS

PRINTING PROCESS MODIFICATIONS 

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Heat Transfer Roller Printing 

Like traditional roller printing, heat transfer printing is done by passing the fabric around a central drum or cylinder where it contacts a roller for transferring the design. The roller is followed by a heating zone to effect the sublimation of the dye. Since all colors are applied to the fabric at the same time, 

however, the operation is simpler with lower processing costs and fewer personnel required. Production can change rapidly from one design to another simply by changing the design paper, whereas in roller or screen printing, each separate roller or screen moved from the machine and the machine set up for a new design with different rollers or screens. Short runs are feasible, fast deliveries are possible, given shorter time for processing, and companies need not keep costly inventories of fabric in stock. On the other hand, heat transfer printing is slower than is either roller or screen printing. 10 to 15 meters of printed fabric are produced per minute in transfer printing operations. 

Heat transfer printing has proved especially successful in printing knitted fabrics. Knitted goods are less dimensionally stable than are woven fabrics. Manufacturers using conventional screen and roller printing techniques on knit fabrics experienced difficulties in making multicolor prints in which the segments of the print must fit together accurately. In transfer printing, all parts of the design are applied at once, eliminating the problem of fabrics stretching as they move from one roller to another. 

Losses of fabric through faulty printing are substantially lower during heat transfer printing than are losses in conventional roller printing. Energy requirements are also lower. Garments and garment pieces can be printed, and precise placement of decorative motifs on a completed garment is possible 

Transfer Printing 

Literally moving a design from one surface to another is known as transfer printing. A typical well-known technique is that of iron-on prints of emblems and decorations, which are generally made of pigments in a paraffin or thermoplastic base that can be melted and bound by heat and pressure onto a fabric surface. These pigment transfers are not very satisfactory because they make the cloth stiff and are not fast to laundering or light. A more sophisticated and effective method of transfer printing is that of transferring a design intact by vaporizing it from the paper to a fabric. There have evolved two principal processes: dry heat transfer and wet heat transfer 

Heat Transfer Printing 

Heat transfer printing, or sublimation printing, is a system in which dyes are printed onto a paper base and then transferred from the paper to a fabric. The transfer of colors takes place as the color vaporizes or “sublimes.” Transfer printing is achieved by rolling or pressing the paper and the fabric together under pressure and at high temperatures (424°F or 200°e). Sublimation printing achieves a sharpness and clarity that other types of printing cannot match. One disadvantage of heat transfer printing, however, is off-grain printing. Some dyes used on nylons and acrylics have displayed variations in shade depth and, in some cases, problems with fastness to laundering. Heat transfer printing also consumes a large quantity or print paper that cannot be reused and may present a disposal problem. Transfer printing can also be used to apply designs to garments such as T-shirts and jackets. Often the design is comprised of pigment colors on a paper sheet. When this is placed on the textile item and a hot press is applied the pigments adhere to the fabric in the design pattern. The design area is usually somewhat stiffer than the rest of the fabric. 

Initially, heat transfer dyes were disperse dyes mostly effective on nylons and polyesters. Disperse dyes can also be used on acrylics, triacetates, and polyester and cotton blends where the proportion of polyester is relatively high. In the early 1990s development of several alternative processes have extended heat transfer printing to silk, cotton and other cellulosic fabrics, and wool.

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Textile Printing methods; Methods Of Direct Printing

Block Printing Methods
The oldest method of printing designs on fabric is block printing by hand. It is not commercially important today because it is too slow––printed fabric cannot be produced inexpensively in large enough quantities by the hand block method. To make blocked prints, the design must first be carved on a wooden or metal block. The dyestuff is applied in paste form to the design on the face of the block. The block is pressed down firmly by hand on selected portions of the surface of the fabric, imprinting the carved design as many times as desired on a specific length of cloth. To obtain variation of color in the same design, as many additional blocks must be carved as there will be additional colors. The portions of the design that will appear in different colors must be separately imprinted by hand before each design is complete. The more colors used, the more valuable and expensive the blocked print will be, because of the enhanced beauty of design as well as the labor involved in the hand printing.

Roller Printing Methods
Roller printing is the machine method of printing designs on cloth by engraved rollers. It turns out color-designed fabrics in vast quantities at the rate of 1000 to 4000 yards (914-3658 m) an hour. This method of producing attractive designs is relatively inexpensive when compared with any hand method. It is a machine counterpart of block printing. In roller printing, engraved copper cylinders or rollers take the place of the hand carved blocks. Just as there must be a separate block for each color in block printing, so must there be as many engraved rollers in machine printing, as there are colors in the design to be imprinted. With each revolution of the roller, a repeat of the design is printed. Engraving is frequently done by pantograph transfer. Separate photographs on individually sensitized copper plates are taken for each color of the design. An artist then paints the appropriate color of the pattern on each plate. The engraver traces the outline of the design on the plate with one arm of a pantograph, plate which simultaneously cuts the design (with a diamond needle on its other arm) into the curved surface of a copper roller. Next, a chemical resistant is coated over the areas of the roller that will print the color, and the roller is treated with acid. The acid etches the unprotected areas, which form the design pattern to be used for color printing.

Each roller is polished for uniform smoothness so that the dye will spread evenly on the raised areas. They are then locked into precise positions on the machine for proper registration (alignment). The number of rollers used depends upon the number of color in the design, and as many as sixteen rollers can be employed.

Each of the engraved rollers first comes in contact with a companion roller that has been submerged in the dye paste to be used for its part of the design. A sharp blade, called the doctor blade, scrapes the excess dye from the surface of the roller. As the fabric passes between the engraved rollers and smooth cylinder rollers, the dye from the shallow areas is passed on it.

Behind and along with the fabric being printed is another fabric, called the back gray, which absorbs the excess print paste and multi color roller printing prevents it from striking through and staining the smooth rollers


The printed cloth is immediately passed into a drying chamber and then into a steam chamber where the moisture and heat sets the dye. The back gray is eventually washed out and reused.

Duplex Roller Printing
Duplex printing is done with rollers on a special machine that imprints designs on both sides of the fabric at the same time. Most often, the same design is printed on opposite sides, although different designs can be printed on each side. The resulting fabric looks like fabric with a woven design. This process is seldom used now, as it is almost as expensive to create duplex prints as it is to weave designs.

Rotary Printing Method
A printing machine that utilizes seamless cylindrical screens made of metal foil was originally developed in Holland. This process is called rotary screen-printing. The machine employs a rotary screen for each color, as in flat screen-printing, and the design for each rotary screen is made in a manner similar to automatic flat screen-printing. As the fabric to be printed is fed under uniform tension into the printer section of the machine, its back is usually coated with an adhesive, which causes it to adhere to a conveyor-printing blanket. Some machines use other means of gripping the cloth firmly in place. The fabric passes under the rotating screens through which the printing paste is automatically pumped from pressure tanks. A squeegee in each rotary screen forces the paste through the screen onto the fabric as it moves along, at rates of up to 100 yards (91 m) per minute.

Rotary screen-printing combines the advantages of roller and flat screen-printing techniques. Rotary metal screens are lightweight in contrast to the heavy copper rolls, and they cost less. They give color depth that is similar to or as good as that of flat screens. Prints of various types and intricate designs with shades of up to twenty colors can be obtained with a high degree of accuracy and sharpness.

Stencil Printing
Stencil printing originated in Japan. Its high cost limits its use and importance in the United States. In stencil printing, the design must first be cut in cardboard, wood, or metal. The stencil may have a fine, delicate design, or there may be large spaces through which a great amount of color can be applied. A stencil design is usually limited to the application of only one color and is generally used for narrow widths of fabric.

Screen Printing Method
Originally, this technique was referred to as silk-screen printing because the screens were made of fine, strong silk threads. Today, they are also made of nylon, polyester and metal. Screenprinting is done with the use of either flat or cylindrical screens.

Flat bed screen printing
Flat bed screen-printing is done commercially on long tables 9 to 60 yards in length. The roll of fabric to be printed is spread smoothly onto the table, whose surface has first bee coated with a light tack adhesive. The print operators then move the screen frames by hand successively along the whole table. Printing one frame at a time, until the entire fabric is printed. Each frame contains one color of the print. The rate of production ranges from 50 to 90 yards per hour by this method. A substantial amount of commercial hand screen-printing is also done on cut garment parts. In printing cut garments, an apparel manufacturer arranges by contract with screen printers Greige Carpet Needle Belt Magnet Color 2 specializing in this service. Customized or unique patterns are printed on garment parts before the pieces are sewn together.

Such items as printed beach towels and novelty printed aprons, draperies, and shower curtains are also printed by hand screen methods because it is possible to make large screen frames for large design repeats.

Hand screen-printing is also used for printing limited-quantity, high-fashion couture as well as for printing small-quantity runs to market-test a design. Flat-bed Zimmer carpet printing machine lays down each color separately form printing paste applied by means of two magnetic roller squeegees. Pressure is controlled by the selection of heavy or light squeegees and by varying the current going to the electromagnet. Endless belts fitted with needles assure a positive drive for good register.

Printing Methods; Methods of textile printing

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Methods of Printing 

There are three basic approaches to printing a color on a fabric. Direct, Discharge and Resist. Transfer Printing is comparatively a new method which is also gaining popularity Direct Printing. The most common approach for applying a color pattern is direct printing. It may be done on a white fabric or over a previously dyed fabric, in which case it is called overprinting. The dye is imprinted on the fabric in paste form, and any desired pattern may be produced. The dyes are usually dissolved in a limited amount of water to which a thickening agent has been added to give the necessary viscosity to the print paste. 

Direct Printing Method

The principle of direct printing is creation of a colored design by applying a dye or pigment directly onto a textile substrate (yarn or fabric). Discharge Printing. Another approach for applying a color pattern is discharge printing. The fabric is dyed in the piece and then printed with a chemical that will destroy the color in designed areas. Sometimes the base color is removed and another color printed in its place, but usually a white area is desirable to brighten the overall design. When properly done, discharge printing gives very good results; however, the discharged areas may literally fall out of the fabric if the goods are not thoroughly washed after printing (a rare situation today). The usual method of producing discharge prints is to print the design, such as polka dots, with a paste containing a reducing agent. A steaming follows and then there is a good washing to remove the by-products of the reaction. Resist Printing A third approach to obtaining a color pattern is resist printing. Bleached goods are printed with a resist paste––a resinous substance that cannot be penetrated when the fabric is subsequently immersed in a dye. The dye will affect only the parts that are not covered by the resist paste. After the fabric has passed through a subsequent dyeing process, the resist paste is removed, leaving a pattern on a dark ground. Their are several other methods also for printing textiles. Two are of significant commercial importance: the screen print method and the roller print method. A third method, heattransfer printing is a comparatively new concept & less significant. Other printing methods rarely used in commercial production of textiles are block, batik, ikat, and resist printing. Many textile printers print fabrics in both screen and roller methods. Most heat-transfer printing is done by printers that specialize in this method. 

Batik 

Batik cloth is made by a wax-resist process. The name batik originates in the Indonesian Archipelago, where resist printing has become an important art form. Wax is applied to the areas that the printer does not want to dye. In Indonesia a small, spouted cup with a handle called a tjanting is used to apply the wax. Melted wax is poured from the tjanting onto the cloth. When it hardens, the wax coats the fabric so that the dye cannot reach the fibers. 

If several colors are to be used, the process becomes somewhat more complex. For example, if a fabric is to be colored white, red, and blue, the artisan begins with a creamywhite cotton cloth. Those areas that are to remain white and those that are to be red are coated with wax. The fabric is now subjected to a blue dyebath, and the exposed areas take on the blue tint. The wax is boiled off and reapplied to cover the blue and white areas. When the fabric is placed in the red dyebath, the color penetrates only the uncovered areas of the design. After dyeing is complete, the fabric is treated with a fixative (a mordant) to make the colors fast, and a final rinse in hot water removes all traces of wax. For faster production a technique was devised whereby the wax could be printed onto the surface of the fabric with a device called a tjap. The design is carved on a tjap block, the block is 

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PRINTING

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Textile Printing

Printing has often been described as dyeing in a localized area to create patterned design. Creating design interest in fabrics can be accomplished in several ways, including yarn variation (novelty yarns). Weave variation (dobby and jacquard), and color effects in weaving. An additional color design can be created through the process of printing design shapes onto previously woven, knitted, or non-woven fabrics. 

Textile printing uses the same dyes or pigments applied to produce dyed fabric. The same principles of specific dye classes having select fiber affinities and the general fastness characteristics apply equally to printing and dyeing. 

The designs for printed fabrics are an important element of the printed fabrics industry. A continuous supply of new designs are required for this highly fashion oriented segment of the textile industry. 

Dyes or pigments used in dyeing are usually in a water bath solution. When the same dyes or pigments are used for printing, they must be thickened with gums or starches to prevent the wicking or flowing of the print design. The thickened solution, about the consistency of heavy buttermilk, is called the print paste. Some dyes cannot be used in printing pastes for reasons such as insufficient solubility and low color yield. 

The application of a pattern to fabric by the use of dyes, pigments, or other colored substances may be effected by a variety of hand or machine processes. Freehand painting of designs on fabrics is probably the oldest technique for applying ornament, but hand painting is a time-consuming procedure. Furthermore, it does not always result in a uniform repeat of a motif that is to be used more than once. If a design is transferred to a Bat surface that can be coated with a dye and then stamped onto the fabric, the same design can be repeated many times over simply by pressing the decorated surface against the fabric. This process is known as printing. Over many centuries a variety of techniques for printing designs have evolved. Printing can be applied to warp yarns, to fabrics, or to apparel pieces-for example, slogans or pictures on T-shirts. 

In general, printing is a cheaper way of creating designs on fabric than weaving or knitting with different colored yarns. Printing can be done with dyes or pigments. For pigments it is necessary to use an adhesive to bind the colored substance to the fabric. Different methods for applying designs can be combined with a number of printing tools or machines to provide the printer with a variety of processes. 

Methods of Printing 

There are three basic approaches to printing a color on a fabric. Direct, Discharge and Resist. 

Direct Printing 

The principle of direct printing is creation of a colored design by applying a dye or pigment directly onto a textile substrate (yarn or fabric). Discharge Printing. Another approach for applying a color pattern is discharge printing. The fabric is dyed in the piece and then printed with a chemical that will destroy the color in designed areas. 

Batik 

Batik cloth is made by a wax-resist process. The name batik originates in the Indonesian Archipelago, where resist printing has become an important art form. Wax is applied to the areas that the printer does not want to dye. 

Methods Of Direct Printing 

Block Printing

The oldest method of printing designs on fabric is block printing by hand. It is not commercially important today because it is too slow 

Roller Printing 

Roller printing is the machine method of printing designs on cloth by engraved rollers. It turns out color-designed fabrics in vast quantities at the rate of 1000 to 4000 yards (914-3658 m) an hour. This method of producing attractive designs is relatively inexpensive when compared with any hand method. 

Rotary Printing 

A printing machine that utilizes seamless cylindrical screens made of metal foil was originally developed in Holland. This process is called rotary screen-printing. 

Screen Printing

Originally, this technique was referred to as silk-screen printing because the screens were made of fine, strong silk threads. Today, they are also made of nylon, polyester and metal. Screen printing is done with the use of either flat or cylindrical screens. 

Heat Transfer Roller Printing 

Like traditional roller printing, heat transfer printing is done by passing the fabric around a central drum or cylinder where it contacts a roller for transferring the design. The roller is followed by a heating zone to effect the sublimation of the dye. Since all colors are applied to the fabric at the same time, 

Other Printing Techniques 

Photographic Printing 

Photographic printing is done in a manner similar to the photochemical preparation of screens for screen printing. A photosensitive dye is coated on the fabric, a negative is placed over the fabric, light is applied, and a photographic type of printing takes place. 

Electrostatic Printing 

Electrostatic printing is an experimental process in which a plate with an electrostatic charge is placed behind the fabric. A stencil in the form of the pattern is placed over the fabric. Special powdered inks that can be attracted by the electrostatic charge are passed over the surface fabric, and the inks are attracted into and color the fabric in the open areas of the stencil. 

Flock Printing 

By imprinting an adhesive material on the surface of a fabric in the desired pattern, and then sprinkling short fibers over the hesive, a flocked print may be created.

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