Textile finishing process is a separate subject a processor should be well versed. This is the end process that adds up value, quality and appearance to the final product.
Each substrate according the end use would finished differently.
Finishing operations can be widely divided into 2 classes; 1) Mechanical means of finishing or mechanical finishes or physical transformation of subtrate due to mechanical processes, 2) Chemical finishes.
Functional Finishes: The properties of synthetic fibers, most important among them being polyamide, polyester and polyacrilonitrile, are essentially different from those of natural cellulosic and wool fibers. Hence the sequence of finishing operations is likely to be different. While cellulosic's require a resin finishing treatment to impart easy-care properties, synthetic fibers already have these easy-care criteria and require only a heat setting operation. The use of 100% synthetic textiles has increased considerably since the arrival texurised yarns consisting of filaments and the growing production of knit goods. The use of open weave has enabled production of lighter, air permeable, fabrics to ensure better wearing comfort.
What is Heat Setting?
Heat setting of synthetic fabrics eliminates the internal tensions within the fiber generated during manufacture and the new state can be fixed by rapid cooling. This heat setting fixes the fabrics in the relaxed state and thus avoids subsequent shrinkage or creasing of fabric. Presetting of goods make it possible to use higher temperature for setting without considering the sublimation properties of dyes and also has a favorable effect on dyeing behavior and running properties of goods. On the other hand, post setting can be combined with some other operations such as thermosol dyeing or optical brightening of polyester, post setting as a final finish is useful to get a high dimensional stability along with desired handle.
The application of heat in heat setting can be done by hot air, on a pin stenter at 220c for 20-30 seconds for polyester goods and at a lower temperature range of 190-225C for 15 -20 seconds for polyamides . Acrylics may be heat set partially at 170-190 c for 15-60 seconds to reduce formation of running creases. but higher temperature should be avoided to prevent yellowing.
Hydro setting is so rarely used particularly to get fuller and softer handle on polyamides at 125-135c in autoclaves for 20-30 minutes. It can be combined with dyeing or optical brightening.
Steam setting can be done by saturated or super heated steam. During steaming, uniform treatment can be ensured by initial sequence of alternate short steaming and vacuum application for 20-30 min at 130C under pressure. Super heated steam can be used in stenters and setting time is 25% shorter than for hot air on account of quicker heating up rate. Acrylic fibers have to be protested as some may under go excessive shrinkage or loss of handle. Before the material is heat set, it should be thoroughly washed to remove spin preparations, lubricants, sizing agents and impurities as these are likely to be burned in drying heat setting making their removal difficult.
Filling and Stiffening finishes:
A stiffening effect is desirable in certain polyamides and polyester materials for petticoats, collar interlinings, etc., which can be done by reducing the mutual independence of structural element of fabric by polymer deposition on coating as a fine film. Some special Urea-formaldehyde pre-condensates have been found to be useful. Application of film-forming acrylates dispersions as well as latex rubber emulsions gives a fuller effect with sufficient stiffness.
When softening is desired it can be achieved by reducing the frictional coefficient between structural elements of fabrics, cationic long chain fatty derivatives and silicones may be used in conjunction with polymer forming agents. Recently some cationic softeners having reactive functional groups have been developed to get better fastness of finish.
On account of lower moisture and water absorption capacity synthetic fiber materials become uncomfortable in contact with skin. Certain products based on modified (oxy-ethylated) polyamides makes the wearing more pleasant by reducing the cohesion of water so that it spreads over a larger area and thus evaporates more rapidly.
Pilling is an unpleasant phenomenon associated with spun yarn fabrics especially when they contain synthetics. Synthetic fibers are more readily brought to the surface of fabric due to their smooth surface and circular cross section and due to their higher tensile strength and abrasion resistance, the pills formed take a long time to be abraded by wear. With knit fabric, two more problems occur, viz., "picking" where the abrasion individual fibers work themselves out of yarn loops onto the surface when garment catches a pointed or rough object. These two effects are more predominant in the weave, is more open and yarn is bulkier.
The finish has to cement the fibers within the yearn so that their dragging becomes more difficult, without affecting the handle adversely. Special polymer formers of acrylate type or latex type are useful but should form a film of good cohesion, should hydrophilic and should not form a tacky surface. padding in polymer dispersion or emulsion followed by drying at moderate temperature gives the desired effect.
Permanent Anti-static effects:
Anti-static effective chemicals are largely chemically inert and require Thermosol or heat treatment for fixing on polyester goods. Agents of polyether type are found to be useful but should not effect the dye-equilibrium on fiber otherwise the rubbing fastness is impaired. In general Thermsolable anti-static agents also have a good soil release action which is as permanent as the anti-static effect. Anti-static finishes may also be of polyamide type being curable at moderate temperatures.
Synthetic warp and weft threads in loosely woven fabrics are particularly prone to slip because of their surface smoothness when the structure of fabric is disturbed and appearance is no loner attractive. To avoid this attempts are made to give the filaments a rougher surface. Silica-gel dispersions or silicic acid colloidal solutions are quite useful and they are used with advantage in combination with latex polymer or acrylates dispersions to get more permanent effect along with simultaneous improvement in resistance to pilling or snagging. These polymer finishes are also capable of imparting a soft and smooth handle to synthetic fabric without imparting water repellency.
Fire Resistant finishes:
With synthetic fiber which melt on igniting by a flame, the molten moss is itself quite dangerous and a fire resistant treatment is desirable for certain end uses. Polyester fabrics can be made flame resistant by treatment with an aqueous emulsion of xylene soluble 2,3-dibromopropyl phosphate in a pad-cure sequence. A semi-permanent effect can be produced by treating with a mixture of ammonium bromide and brominated phosphoric acid esters.
Polyamides can be made flame resistant by applying phosphorous tri-chloride ammonia reaction products or ammonium bromide with amino-triazine condensation products. For acrylics tris-dibromopropyl-phosphate as well as 2-cyanoethyl-tetramethyl-di-amino-phosphate is quite effective.
With the increasing use synthetic fibers for carpets and other materials in public places, anti-microbial finishes have assumed importance. A reduction in soiling tendency will along way in keeping textiles free from germs and usual soil repellant as well as soil release finishes are effective in some way. products which are commonly applied are brominated phenols, quaternary ammonium compounds, organo-silver and tin compounds which can be applied as solutions or dispersions. They can also be incorporated in a polymeric film deposited on the surface to get controlled release. Some reactive systems similar to those for reactive dyes have been recently tried to incorporate anti-microbial structural features.
Finishing of Elastomeric textiles:
The heat sensitivity of electrometric fibers limits the choice of products and finishing process that can be employed. In order to eliminate the latent tensions, these electrometric textiles are simply steamed or treated with hot water. Dry curing or heat treatment is restricted to temperature below 140C,. These fabric have e to be dried and curd with minimum tension with over feed stenter. To groups of materials, viz., foundation fabric and knitted fabric for bathing snits are resin finished. Water proofing can be imparted by using Zirconium salts containing wax emulsions as it does not require a high temperature treatment. A filling treatment can be obtained with modified methylol-urea type products.