Basic methods and processes
The term finishing includes all the mechanical and chemical processes employed commercially to enhance the acceptability of the merchandise , except those procedures directly concerned with colouring. the target of the varied finishing processes is to form fabric from the loom or knitting frame more acceptable to the buyer . Finishing processes include preparatory treatments used before additional treatment, like bleaching before dyeing; treatments, like glazing, to reinforce appearance; sizing, affecting touch; and coverings adding properties to reinforce performance, like preshrinking. Newly formed cloth is usually dirty, harsh, and unattractive, requiring considerable skill for conversion into a desirable product. Before treatment, the unfinished fabrics are mentioned as gray goods, or sometimes, within the case of silks, as greige goods.
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Finishing formerly involved a limited number of comparatively simple operations evolved over the years from hand methods. The skill of English and Scottish finishers was widely known , and far British cloth owed its high reputation to the expertise of the finisher. More sophisticated modern finishing methods are achieved through intense and imaginative research.
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Preparatory treatments
It is frequently necessary to hold out some preparatory treatment before the appliance of other finishing processes to the newly constructed fabric. Any remaining impurities must be removed, and additives wont to facilitate the manufacturing process must even be removed. Bleaching could also be required to extend whiteness or to organize for colour application. a number of the foremost frequently used preparatory processes are discussed below.
Burling and mending
Newly made goods, which regularly show imperfections, are carefully inspected, and defects are usually repaired by hand operations. the primary inspection of woollen and worsted fabrics is named perching. Burling, mainly applied to woollen, worsted, spun rayon, and cotton fabrics, is that the process of removing any remaining foreign matter, like burrs and, also, any loose threads, knots, and undesired slubs. Mending, frequently necessary for woollens and worsteds, eliminates such defects as holes or tears, broken yarns, and missed warp or weft yarns.
Scouring
When applied to gray goods, scouring removes substances that have adhered to the fibres during production of the yarn or fabric, like dirt, oils, and any sizing or lint applied to warp yarns to facilitate weaving.
Bleaching
Bleaching, a process of whitening fabric by removal of natural colour, like the tan of linen, is typically administered by means of chemicals selected consistent with the chemical composition of the fibre. Chemical bleaching is typically accomplished by oxidation, destroying colour by the appliance of oxygen, or by reduction, removing colour by hydrogenation. Cotton and other cellulosic fibres are usually treated with heated alkaline peroxide ; wool and other animal fibres are subjected to such acidic reducing agents as gaseous sulphur dioxide or to such mildly alkaline oxidizing agents as hydrogen peroxide. Synthetic fibres, once they require bleaching, could also be treated with either oxidizing or reducing agents, depending upon their chemical composition. Cottons are frequently scoured and bleached by endless system.
Mercerization
Mercerization may be a process applied to cotton and sometimes to cotton blends to extend lustre (thus also enhancing appearance), to enhance strength, and to enhance their affinity for dyes. the method , which can be applied at the yarn or fabric stage, involves immersion under tension during a sodium hydroxide (sodium hydroxide) solution, which is later neutralized in acid. The treatment produces permanent swelling of the fibre.
Drying
Water, utilized in various phases of textile processing, accumulates in fabrics, and therefore the excess moisture must eventually be removed. Because evaporative heating is expensive , the primary stage of drying uses mechanical methods to get rid of the maximum amount moisture as possible. Such methods include the utilization of centrifuges and endless method employing vacuum suction rolls. Any remaining moisture is then removed by evaporation in heated dryers. Various sorts of dryers operate by conveying the relaxed fabric through the chamber while festooned in loops, employing a frame to carry the selvages taut while the material travels through the chamber, and spending the material over a series of hot cylinders. Because overdrying may produce a harsh hand, temperature, humidity, and drying time require careful control.
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Finishes enhancing appearance
Treatments enhancing appearance include such processes as napping and shearing, brushing, singeing, beetling, decating, tentering, calendering or pressing, moiréing, embossing, creping, glazing, polishing, and optical brightening.
Napping and shearing
Napping may be a process which will be applied to woollens, cottons, spun silks, and spun rayons, including both woven and knitted types, to boost a velvety, soft surface. the method involves passing the material over revolving cylinders covered with fine wires that lift the short, loose fibres, usually from the weft yarns, to the surface, forming a nap. the method , which increases warmth, is usually applied to woollens and worsteds and also to blankets.
Shearing cuts the raised nap to a consistent height and is employed for an equivalent purpose on pile fabrics. Shearing machines operate very similar to rotary lawn mowers, and therefore the amount of shearing depends upon the specified height of the nap or pile, with such fabrics as gabardine receiving very close shearing. Shearing can also be applied to make stripes and other patterns by varying surface height.
Brushing
This process, applied to a good sort of fabrics, is typically accomplished by bristle-covered rollers. the method is employed to get rid of loose threads and short fibre ends from smooth-surfaced fabrics and is additionally wont to raise a nap on knits and woven fabrics. Brushing is usually applied to fabrics after shearing, removing the cut fibres that have fallen into the nap.
Singeing
Also called gassing, singeing may be a process applied to both yarns and fabrics to supply a good surface by burning off projecting fibres, yarn ends, and fuzz. this is often accomplished by passing the fibre or yarn over a gas flame or heated copper plates at a speed sufficient to burn away the protruding material without scorching or burning the yarn or fabric. Singeing is typically followed by passing the treated material over a wet surface to assure that any smoldering is halted.
Beetling
Beetling may be a process applied to linen fabrics and to cotton fabrics made to resemble linen to supply a tough , flat surface with high lustre and also to form texture less porous. during this process, the material , dampened and wound around an iron cylinder, is skilled a machine during which it's pounded with heavy wooden mallets.
Decating
Decating may be a process applied to woollens and worsteds, synthetic and blended fibre fabrics, and various sorts of knits. It involves the appliance of warmth and pressure to line or develop lustre and softer hand and to even the set and grain of certain fabrics. When applied to double knits it imparts crisp hand and reduces shrinkage. In wet decating, which provides a subtle lustre, or bloom, fabric under tension is steamed by passing it over perforated cylinders.
Tentering, crabbing, and heat-setting
These are final processes applied to line the warp and weft of woven fabrics at right angles to every other, and to stretch and set the material to its final dimensions. Tentering stretches width under tension by the utilization of a tenter frame, consisting of chains fitted with pins or clips to carry the selvages of the material , and travelling on tracks. because the fabric passes through the heated chamber, creases and wrinkles are removed, the weave is straightened, and therefore the fabric is dried to its final size. When the method is applied to wet wools it's called crabbing; when applied to synthetic fibres it's sometimes called heat-setting, a term also applied to the permanent setting of pleats, creases, and special surface effects.
Calendering
Calendering may be a final process during which heat and pressure are applied to a cloth by passing it between heated rollers, imparting a flat, glossy, smooth surface. Lustre increases when the degree of warmth and pressure is increased. Calendering is applied to fabrics during which a smooth, flat surface is desirable, like most cottons, many linens and silks, and various synthetic fabrics. In such fabrics as velveteen, a flat surface isn't desirable, and therefore the cloth is steamed while in tension, without pressing. When applied to wool, the method is named pressing and employs heavy heated metal plates to steam and press the material . Calendering isn't usually a permanent process.
Moiréing, embossing, glazing and ciréing, and polishing are all variations of the calendering process. Moiré may be a wavy or “watered” effect imparted by engraved rollers that press the planning into the material . the method , applied to cotton, acetate, rayon, and a few ribbed synthetic fabrics, is merely permanent for acetates and resin-treated rayons. Embossing imparts a raised design that stands out from the background and is achieved by passing the material through heated rollers engraved with a design. Although embossing was formerly temporary, processes have now been developed to form this effect permanent.
Glazing imparts a smooth, stiff, highly polished surface to such fabrics as chintz. it's achieved by applying such stiffeners as starch, glue, shellac, or resin to the material then passing it through smooth, hot rollers that generate friction. Resins are now widely employed to impart permanent glaze. Ciré (from the French word for waxed) may be a similar process applied to rayons and silks by the appliance of wax followed by hot calendering, producing a metallic high gloss. Ciré finishes are often achieved without a sizing substance in acetates, which are thermoplastic (e.g., are often softened by heat), by the appliance of warmth .
Polishing, wont to impart sheen to cottons without making them as stiff as glazed types, is typically achieved by mercerizing the material then passing it through friction rollers.
Creping
A crepe effect could also be achieved by finishing. In one method, which isn't permanent, the material is passed, within the presence of steam, between hot rollers crammed with indentations, producing waved and puckered areas. within the more permanent sodium hydroxide method, a sodium hydroxide paste is rolled onto the material during a patterned form, or a resist paste could also be applied to areas to stay unpuckered, and therefore the entire fabric is then immersed in sodium hydroxide . The treated areas shrink, and therefore the untreated areas pucker. If the pattern is applied within the sort of stripes, the effect is named plissé; an allover design produces blister crepe.
Optical brightening
Optical brightening, or optical bleaches, are finishes giving the effect of great whiteness and brightness due to the way during which they reflect light. These compounds contain fluorescent colourless dyes, causing more blue light to be reflected. Changes in colour may occur because the fluorescent material loses energy, but new optical whiteners are often applied during the laundering process.
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Finishes enhancing tactile qualities
Finishes enhancing the texture and drape of materials involve the addition of sizing, weighting, fulling, and softening agents, which can be either temporary or permanent.
Sizing
Sizing, or dressing, agents are compounds that form a movie round the yarn or individual fibres, increasing weight, crispness, and lustre. Sizing substances, including starches, gelatin, glue, casein, and clay, are frequently applied to cottons and aren't permanent.
Weighting
Weighting, within the processing of silk, involves the appliance of metallic salts to feature body and weight. the method isn't permanent but are often repeated.
Fulling
Also called felting or milling, fulling may be a process that increases the thickness and compactness of wool by subjecting it to moisture, heat, friction, and pressure until shrinkage of 10 to 25 percent is achieved. Shrinkage occurs in both the warp and weft, producing a smooth, tightly finished fabric which will be so compact that it resembles felt.
Softening
Making fabrics softer and sometimes also increasing absorbency involves the addition of such agents as dextrin, glycerin, sulfonated oils, sulfated tallow, and sulfated alcohols.
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Finishes improving performance
The performance of materials in use has been greatly improved by the event of processes to regulate shrinkage, new resin finishes, and new heat-sensitive synthetic fibres.
Shrinkage control
Shrinkage control processes are applied by compressive shrinkage, resin treatment, or heat-setting. Compressive, or relaxation, shrinkage is applied to cotton and to certain cotton blends to scale back the stretching they experience during weaving and other processing. the material is dampened and dried during a relaxed state, eliminating tensions and distortions. the amount of warp and weft yarns per sq in is increased, contributing greater durability, and fabrics treated by this method are usually smooth and have soft lustre. the method involves spraying the material with water then pressing the material against a steam-heated cylinder covered with a thick blanket of woollen felt or rubber. The manufacturer is usually required to specify the residual shrinkage, or percentage of shrinkage, which will still occur after the preshrinking process.
Rayons and rayon blends could also be stabilized by the utilization of resins, which impregnate the fibre. Such fabrics can also be stabilized by employing acetals to supply cross-linking, a reaction . Such synthetics as polyesters and nylons, which are heat sensitive, are usually permanently stabilized by heat-setting during finishing.
Shrinkage of wools is usually controlled by treatment with chlorine, partially destroying the scales that occur on wool fibres and thus increasing resistance to the natural tendency of wool to felt. Other methods employ coating with resins that attach to the scales so as to discourage felting shrinkage.
Durable press
Durable press fabrics have such characteristics as shape retention, permanent pleating and creasing, permanently smooth seams, and therefore the ability to shed wrinkles, and thus retain a fresh appearance without ironing. Such fabrics could also be safely washed and dried by machine. These useful characteristics are imparted by a curing process. Depending upon composition and desired results, fabrics could also be precured, a process during which a chemical resin is added, the material is dried and cured (baked), and warmth is applied by pressing after garment construction; or fabrics could also be postcured, a process during which resin is added, the material is dried, made into a garment, pressed, then cured.
Wash-and-wear was an early permanent press process employing chemical treatment and curing of fabrics; a minimum of light ironing was required to revive appearance. Later, however, processes were developed that allowed such fabrics to regain smoothness after home machine washing at moderate temperature, followed by tumble drying.
Crease resistance
Crease, or wrinkle, resistance is usually achieved by application of an artificial resin, like melamine or epoxy.
Soil release
Soil release finishes facilitate removal of waterborne and oil stains from fabrics like polyester and cotton blends and fabrics treated for permanent press , which usually show some resistance to stain removal by normal cleaning processes. Other finishes are developed that give fabrics resistance to water and oil stains.
Antistatic finishes
The accumulation of electricity in such synthetic fibres as nylon, polyesters, and acrylics produces clinging, which can be reduced by application of permanent antistatic agents during processing. Consumers can partially reduce electricity by adding commercial fabric softeners during laundering.
Antibacterial and antifungus finishes
Antibacterial finishes are germicides applied to fabrics to stop odours produced by bacterial decomposition, like perspiration odours, and also to scale back the likelihood of infection by contact with contaminated textiles. Fabrics can also be treated with germicides to stop mildew, a parasitic fungus which will grow on fabrics that aren't thoroughly dried. Both mildew and decay , another sort of decay, can also be controlled by treatment with resins.
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Moth-repellent treatments
Wool and silk are subject to attack by moths but could also be made moth repellent by the appliance of appropriate chemicals either added within the dye bath or applied to the finished fabric.
Waterproofing and water repellence
Waterproofing may be a process applied to such items as raincoats and umbrellas, closing the pores of the material by application of such substances as insoluble metallic compounds, paraffin, bituminous materials, and drying oils. Water-repellent finishes are surface finishes imparting a point of resistance to water but are easier to wear because the material pores remain open. Such finishes include wax and resin mixtures, aluminum salts, silicones, and fluorochemicals.
Flameproof, fireproof, and fire-resistant finishes
Flameproof fabrics are ready to withstand exposure to flame or heat . this is often achieved by application of varied finishes, depending upon the material treated, that cause burning to prevent as soon because the source of warmth is removed. Fireproofing is achieved by the appliance of a finish which will stop the oxygen supply round the flame. Fire-resistant finishes cause fabrics to resist the spread of flame.