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Textile coating
This document discusses textile coating, which involves applying a polymeric layer to fabric surfaces to enhance properties. It defines coating and describes common polymers, physical forms, and coating processes used. Key coating methods covered are direct coating, foam coating, transfer coating, hot melt extrusion, and calendar coating. The document also outlines factors considered for substrate selection and coating uniformity. Various applications of coated fabrics are provided across multiple industries.
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Textile coating
- 1. By, Pranay Kumar Sabat TexportSyndicate (India) Ltd TEXTILE COATING
- 2. INTRODUCTION *Coating has nowbecome a very important technique for adding value to textiles. *Coating enhances and extends the range of functional properties of textiles. *The use of these techniques is growing rapidly as the applications for technical textile material has become more diverse.
- 3. DEFINITION *Coating is anapplication of appropriate chemical system to form a layer of a coating compound on the substrate. *This is a process in which a polymeric layer is applied directly on one or both surfaces of the fabric. *Various type of coatings are applied depending on the end-use *Formulation contains various chemicals depending on *End use requirement *Nature of polymer *Necessary additives for the specific end use *Type of coating machinery to be used
- 4. POLYMERS USED *Polyvinyl Chloride(PVC) *Polyvinylidene chloride (PVDC) *Polyurethane (PU) *Acrylic *Ethylene Vinyl Acetate (EVA) *Poly Tetra Fluoro Ethylene (PTFE) *Styrene Butadine Rubber (SBR) *Silicone *Polyolefins, LDPE, HDPE, Polypropylene
- 5. PHYSICAL FORMS OFCOATING COMPOUNDS *Solvent based systems *Water based Systems – dispersions and emulsions *100% solid materials- Film, Powder, Hot melt
- 6. COATING PROCESS Substrate CoatingDrying Curing
- 7. SUBSTRATE *A wide rangeof textile materials is used as substrates for coating *Woven *Knitted *Nonwoven material *Cotton, Rayon, Nylon, Polyester and blends. *Polyester is the most popular in staple form for nonwoven material and also in spun form for woven material. *Polypropylene is emerging as the fiber of choice owing to its low specific gravity, strength properties, chemically inert nature and low cost.
- 8. SELECTION OF FABRIC Thefollowing factors are considered *Strength and modulus *Creep behaviour *Chemical resistance *Adhesion requirements *Resistance to biological activities *End use environment *Durability requirement *Dimensional stability *Cost
- 9. PARAMETERS FOR UNIFORMITY Theparameters necessary for coating uniformity are as follows *Substrate tension *Substrate uniformity *Viscosity of coating material *Coating technology
- 10. SELECTION OF METHODS Themethod or technique to be used for coating to produce any product is determined by *Required add on *The nature of the compound to be applied in terms of its viscosity and other physical characteristics *The degree of penetration required into the substrate *Cost that can be accepted in the end product
- 11. COATING METHODS *Direct *Foamed andcrushed foam *Transfer *Hot melt extrusion *Calender *Spray *Dry Powder *Curtain *Slot die or extrusion *Mayer rod *Kiss roll *Gravure roll *Reverse roll
- 12. DIRECT / KNIFECOATING *Direct application of coating fluid is done by uniform spreading of coating by means of a fixed knife. *The gap between bottom of knife and surface of fabric determines the thickness of the coating. *The main techniques used are as follows *Knife on air *Knife over roller
- 13. KNIFE ON AIR *Thistype of knife coating is a blade over air, or floating knife process *The blade presses the upper surface of the fabric and forces the coating layer to penetrate into the substrate *The sharpness of the blade, alignment angle and degree of depression into the substrate, influence the amount of coating applied.
- 14. KNIFE OVER ROLLER *Inthis process the knife is suspended over the roller. *The gap between the knife and substrate surface over roller determines the coating add on. *This method has a better control over uniformity of the coat but has a lesser production speed as compared to Knife on Air method.
- 15. CRUSHED FOAM COATING *Foamwhich is like a shaving cream, sits on the top of the fabric and is then crushed by a roller to apply the coating. *The method can apply polymer to woven fabrics, knitted fabrics or fabrics with an open construction which can not be directly coated. *Much softer and drapable fabric handle can be achieved when compared to direct coating. *Applications- Apparels, Floor coverings, wall coverings, curtain linings and black out curtains etc.
- 16. CRUSHED FOAM COATING Foam generator Knifeon roll Coating Stenter drying Stainless steel crushing rolls Stenter Curing Polymer Emulsion + Foaming agents
- 17. TRANSFER COATING *The principleof transfer coating is first to spread the polymer onto release paper to form a film and then to laminate this film to the fabric. The process can be explained in few steps as below 1. Coat the resin (which will be the top layer) on to the transfer paper and evaporate off the solvent. 2. Coat on the second layer ( which will become the base layer and is actually the adhessive which joins the top layer to the fabric) 3. Lay the fabric on top of the coating, nip together, evaporate the solvent and crosslink the layers together. 4. Peel the release paper off the coated fabric. *Applications- Footwear, Gloves, waterproof mattress covers and automotive upholsteries.
- 18. TRANSFER COATING PROCESS 1-Release Paper 2- First coating head 3- First oven 4- Second coating head 5- Textile substrate 6- Nip rolls 7- Second drying rolls 8- Coated fabric take off roll 9- Release paper wind roll
- 19. HOT MELT EXTRUSIONCOATING *This method is used for thermoplastic polymers such as polyurethane, Polyolefins and PVC. *These are applied by feeding molten granules of the material into the nip between moving rolls. *This method can apply resin (in the form of film) to fabric at a faster rate than transfer coating or direct coating. *This is very cost effective. *Applications- tarpulins, light weight coverings etc.
- 20. CALENDER COATING *Calenders areused to produce unsupported films of PVC and rubbers from compounded polymer dough (feedstock). *These consists of a number of heavy rollers. *Rollers rotate to crush the dough and smoothen it into films of uniform thickness which is then applied on the substrate. *The thickness of the film is determined by the gap between the calender rollers.
- 21. SPRAY COATING *In thismethod, a coating material is sprayed onto the substrate. *Spray coating methods are * Compressed air vaporisation * Airless pressure spray * Hot vapour impelled spray * Elecrostatic spray * Dry powder resin spray *Limitations * Lack of uniformity and precision * Occasional blocking of spray nozzle
- 22. DRY POWDER COATING *Theseprocesses are used to coat fusible polymer powders like Polyethylene, Polyamide, polyester and Ethylene vinyl acetate (EVA) *There are basically two types of powder coating * Scatter coating process- Polymer powder is spread uniformly onto a moving textile substrate. The web is then passed through a fusion oven and then calendered. * Powder dot coating process- A heated web having a surface temperature slightly less than the melting point of the polymer is brought in contact with an engraved roll embeded with dry powder. The web is thus coated with a tacky polymer powder in a pattern as per the engraved roll. The engraved roll is kept cool to prevent the powder sticking to it.
- 23. CURTAIN COATING *In curtaincoating the coating fluid forms a free falling liquid sheet and is deposited onto a moving substrate. *No friction is involved so the coating fluid is not forced to penetrate the substrate structure but follows the surface to form a film. *Preventing air entrapment and establishing stable fluid curtains are the keys to achieving a quality coating.
- 24. SLOT DIE OREXTRUSION COATING *In this method thermoplastic polymer is pressed through a sheeting die and transferred directly onto the substrate to be coated. *In this system the die lip is in contact with the substrate backed by a pressure roller. *This is a closed system having no contact between air and the coating material
- 25. MEYER ROD COATING *Inthis method, compound is applied on the web by a single roll applicator. *An excess of the coating is deposited onto the substrate as it passes over the bath roller. *The coating is post metered by a wire wound rod, known as the meyer rod that removes excess coating.
- 26. KISS ROLL COATING *Coatingis applied on the substrate as it passes through the nip of the applicator roll and back up roll. *The pick up roll and applicator rolls are rubberised and the back up roll is made up of steel surface. *The metering is done by nip pressure, and consequently the amount of material coated on the fabric is dependent on Nip pressure, speed of the operation, roll hardness and its finish.
- 27. GRAVURE ROLL COATING *Engraveddots or lines of the engraved roll pick up the coating paste and gets filled by it. *The excess coating is wiped off by the doctor blade. *Coating is deposited on the substrate as it passes between the engraved roller and the pressure roller.
- 28. REVERSE ROLL COATING *Coatingmaterial is metered onto the nip of metering roll and the application roll. *The coating is taken up by the substrate as it passes through the nip of application roll and the support roll.
- 29. APPLICATIONS OF COATEDFABRICS AGRICULTURE Bulk containers, Fencing, seed/crop covers, bags, irrigation system.
- 30. APPLICATIONS OF COATEDFABRICS CONSTRUCTION Safety fencing, wind covers, hose, conveyor belts, architectural structures.
- 31. APPLICATIONS OF COATEDFABRICS CLOTHING Shoe uppers and linings, artificial leather, rainwear, garment linings, gloves, hats.
- 32. APPLICATIONS OF COATEDFABRICS GEOTEXTILES Settling pond liners, irrigation liners, landfill liners and covers, soil stabilisers, erosion barriers
- 33. APPLICATIONS OF COATEDFABRICS HOME FURNISHING Upholstery, carpets, drapery backings, beddings, artificial leather
- 34. APPLICATIONS OF COATEDFABRICS INDUSTRIAL Conveyor belts, filtration, barrier materials, Field covers
- 35. APPLICATIONS OF COATEDFABRICS MEDICAL, AUTOMOTIVE, SPORTS Implants, plasters, gloves, seat covers, carpets, athletic shoes, balls
- 36. APPLICATIONS OF COATEDFABRICS PACKAGING Bulk containers, barrier packaging, liquid storage, waterproof materials
- 37. ADVANCED COATINGS *Phase changematerial coating *Smart conductive coatings *Flame retardant coatings *Antibacterial coatings *Ultra ever-dry coating