Introduction

Coating
➢ Polymer or elastomer, usually in viscous form, is applied directly
onto the fabric and cured. A variety of techniques are used.

➢ This process is used to improve the performance of textiles or/and

impart specific charactertistics.
➢ The factors influencing the performance of coated fabrics are
➢ The polymer and the ingredients of formulation used for coating
➢ The substrate: the properties of fabric
➢ The coating method
Introduction
Laminating:
A pre-made or extruded film is bonded onto the substrate, generally
with thermal or adhesive bonding. Curing is generally not required.
Introduction
Reasons to coat textiles

 Air impermeability
 Waterproofing
 Fire proofing
 Conductivity
 Thermal insulation
 UV protection
 Shielding from electromagnetic interference (EMI)
 Antimicrobial properties
 Self-cleaning
Introduction
 Application of coated fabric

 Industrial applications
 Outdoor and sports
 Automotive industry
 Outwear and foor wear
 Construction and infrastructure
 Personnel protective equiment
 Healthcare
 Furnitire and upholestry
 Agriculture
 Packaging
 Aerospace
Introduction
Properties:
 Manufacturing and processing
Conveyer belts Pond lining ▪Chemical resistance
▪Thermal stability
▪Fire resistance
▪Waterproof
▪Thermal insulation
▪Food grade

Industrial hose Tank covers

Introduction
 Transportation applications
Properties:
Tarpaulin Airbags Lifejackets
▪Abrasions resistance
and durability
▪Fire resistance
▪Good tear strength
▪Thermal stability
▪Waterproofing

Convertible tops Inflatable boats

Seat covers
Introduction
 Agricultural applications
Tarpaulin (food grains Collection of fruits
covers)
Properties:

▪Fire resistance
▪Waterproof
▪ UV protection

Collapsable bags Biogas bags

Introduction
 Construction Applications

Properties:
•Waterproof
•Fire resistance
•Good tear strength
•Thermal insulating
▪ UV resistance
Introduction
Properties:
 Sports and leisure applications
Sailcloth Balloon fabric •Waterproof
•UV resistance
•Fire resistance
•Good tear strength
•Abrasion resistant and
durable
•Thermal insulating
•Thermal stability

Paraglider fabric Sleeping bags

Introduction
 Personal and property protection Applications

Biological, gas, and chemical protection

Protective clothing and chemical- resistant gloves
Fire and heat protection
Properties:
Extreme cold protection
Electrostatic protection
•Good tear strength
•Chemical and fire
resistance
•Thermal stability
•Waterproof
•Thermal insulating
•Electrical insulating
•EMI
Introduction
Properties:
 Decoration
Artificial leather •Good abrasion resistance
•Chemical and fire resistance
•Waterproof
•Water and oil repellent

Curtains
Table cloth
Coating Materials
Polyvinyl chloride (PVC)
 PVC is produced from vinyl chloride monomer by
using free radical polymerization technique

CH2=CH-Cl → -CH2-CH-
Cl

 The molecular weight ( M n) of commercial PVC,

ranges from 50,000 to 100,000
 Has 10% crystallinity and considered as amorphous
polymer
 It is a white, water-insoluble thermoplastic resin
 Mainly used for coatings, insulation and piping
Polyvinyl chloride (PVC)
 Low price
 Glass Transition Temperature Tg is 85 °C
 No specific melting point, It decomposes at 220 °C
 Dimensional stability up to its Tg
 Good creep resistance, low shrinkage, good impact
resistance
 PVC is relatively unstable to heat (releases HCl) and
ultraviolet (UV) light
Polyvinyl chloride (PVC)
Processing of PVC  Additives
 Good resistance to oil,  Plasticizer
solvent and abrasion  Heat stabilizers
 PVC has inheret fire  Fillers
retardancy  Lubricants
 Difficult to process alone due  Colors
to low thermal stability and  Flame retardants
high viscosity  Others
 Various additives are used to
make it processable and to
impart required properties
Polyvinyl chloride (PVC)
Plasticizers
 These are liquids of low or negligible volatility or low
molecular weight solids
 Used to yield materials with properties ranging from rigid
to soft and flexible
 It lowers the glass transition temperature
 It can be few percent to 60% depending upon requirement
 Plasticizers can be of two types
 Internal plasticizers
Appropriate copolymers to alter the main molecular structure of
the main polymer chain (vinyl chloride-vinyl acetate copolymer
 External plasticizers
Liquids of negligibly low volatility that are compatible with the
polymer
Polyvinyl chloride (PVC)
 Characteristics of Plasticizers
 Compatibility
Compatibility can also be determined from clear point, which is
the temperature at which the PVC, plasticizer mixture becomes
clear. The lower the clear point temperature, the greater the
compatibility. On the basis of compatibility, plasticziers can be
calssified as;
• Primary Plasticizers

• Secondary Plasticizers

 Efficiency
The amount of plasticizer required for specific property or the
reduction in Tg.
 Permanance
Should not be lost or migrate under usage conditions
Polyvinyl chloride (PVC)
 Commonly used plasticizers
 Phthalates (mainly C8, including di-2-ethylhexyl phthalate and
diisoctyl phthalate)
 Most widely used
 The lower chain length esters have high solvating power but suffer from high
volatility
 Poor low temperature properties
 Phosphates (mainly oganic esters of phosphoric acid)
 The triaryl phosphates offer excellent flame retardance, good solvating power,
and good compatibility, but poorer low temperature properties.
 Polymeric plasticizers Liquid composition
 The majority of commercial plasticizers of this class are saturated polyesters
 Higher molecular weight, higher permanance and lower volatility but low
compatibility
 Epoxies
 Epoxidized soybean oil and linseed oil exhibit good plasticizing and stabilizing
actions.
 They possess low volatility and good resistance to extraction.

 Liquid composition of PVC with plasticizers is called PLASTISOL

Polyvinyl chloride (PVC)
PLASTISOLS AND ORGANOSOLS
 These are fluids in which fine PVC particles are
dispersed in plasticizers
 Plastisol does not contain any solvent or volatile compounds
 An organosol is a plastisol containing volatile organic solvents

 PVC pastes have two important characteristics

 They are liquids and can be processed in that condition. The
processing conditions are determined by the property of the paste
at ambient temperature.
 On application of heat, when required, they fuse to viscous
solutions of polymer in plasticizer, and on cooling, they result in
plasticized PVC.
Polyvinyl chloride (PVC)
Heat Stabilizers
 PVC is heat sensitive and undergoes degradation when
heated to Tg
 During the process, the PVC undergoes the following
changes at high temperature
➢ dehydrochlorination

➢ Crosslinking

➢ Chain scission
Polyvinyl chloride (PVC)
 Dehydrochlorination
Polyvinyl chloride (PVC)
 Crosslinking and chain scission
Polyvinyl chloride (PVC)
Mechanism of Heat Stabilization

 Reaction with allylic chlorine atom

 Scavenging the hydrogen chloride generated by

degradation
Polyvinyl chloride (PVC)
Commonly used Heat Stabilizers

 Alkyltin Stabilizers

 Mixed Metal Stabilizers

 Alkyl Phosphites Stabilizers

 Epoxidized Fatty Acid Esters Stabilizers

 Hydrotalcites Stabilizers
Polyvinyl chloride (PVC)
 Alkyltin Stabilizers
 Tin alkyl thioglycolates
 They react with hydrogen chloride
Polyvinyl chloride (PVC)
 Mixed Metal Stabilizers

The mechanism depends on the type of metals:

1) Strongly basic carboxylates derived from K, Ca,

are HCl scavenger

2) Metals such as Zn and Cd, which are stronger Lewis

acids and form covalent carboxylates, not only scavenge

HCl, but also substitute carboxylate for the allylic chlorine

atoms.
Polyvinyl chloride (PVC)
Mechanism of Mixed Metal Stabilizers
Polyvinyl chloride (PVC)
 Trialkyl phosphites scavenge HCl form dialkyl
phosphites. They also react with allylic chlorides,
but this process plays a secondary role
Polyvinyl chloride (PVC)
Epoxides
 These are HCl scavengers and are also reported to
be effective in allylic chlorine replacement in the
catalytic presence of Zn and Cd salts
Polyvinyl chloride (PVC)
Hydrotalcites
 Hydrotalcite, a natural mineral, is the
hydroxycarbonate of Mg and Al with the exact
formula: Mg6Al2 (OH)16CO3.4H2O.
 Hydrotalcite-like clays with anions of weak acids
react with strong acids such as HCl and exchange
the anions with Cl-.
 This reaction allows hydrotalcite-like clays to be
used as HCl scavengers in PVC stabilization
Polyvinyl chloride (PVC)
Fillers
 Used for reduction of cost by replacing the more
expensive polymer
 better processability
 Enhance functional characteristics
 The common fillers are
 Calcium carbonate fillers—whiting, and marble dust,
 Silicates—clay, talc, and asbestos
 Barytes
Polyvinyl chloride (PVC)
Lubricants
 The lubricants prevents the sticking of molten PVC
and improves release from hot metal processing
equiment
 Commoly used lubricants
 Mineral oil, silicone oils, vegetable oils, and waxes are
common lubricants.
Polyvinyl chloride (PVC)
Viscosity Depressants
 These are surface-active agents
 They lower the viscosity and improve viscosity stability
and air release properties
 Polyethylene glycol derivatives are generally effective
Polyvinyl chloride (PVC)
Thickeners
 For certain applications, paste should have a high
viscosity at low shear rates and a low viscosity at high
shear rate.
 Various thickening agents like fumed silica, special
bentonites, and aluminium stearates are used
 These form a gel structure and are also known as
plastigels
Polyvinyl chloride (PVC)
Blowing Agents
 They are used to produce expanded PVC
 The commonly used blowing agent is azo dicarbonamide, which
decomposes to form nitrogen gas
 The decomposition of the blowing agent should occur at or above the
fusion temperature for the formation of a closed-cell structure
Polyvinyl chloride (PVC)
Colorants
 The colorants of PVC are inorganic and organic
pigments.
 The inorganic pigment like titanium dioxide have
excellent heat resistance, light stability.
 The organic pigments are phthalocyanines,
quinacridines, and benzidines
Polyvinyl chloride (PVC)
Flame retardants
 The inherent flame retardant property of PVC due to
the presence of a chlorine atom is affected by the
addition of flammable plasticizers.
 Antimony trioxide and borates of zinc and barium are
widely used to enhance flame retardency of PVC.
Polyvinyl chloride (PVC)
Manufacturing Recipe
 The pastes are made in a simple paddle-type mixer that
provides an intermediate level of shear
 The temperature should not rise during mixing
 The presence of air may result in bubbles and loss of clarity
of the end product
 Therefore, mixing is done in vacuum
Polyvinyl chloride (PVC)
Fusion
Polyvinyl chloride (PVC)
UV Stability E=nhc/λ
Type Wavelength(nm) Energy kJ/mole
Far UV 100 1196
Vacuum UV 200 598
Mid-range UV 350 341
End of UV range 390 306
Blue/green light 500 239

Bond Strength, kJ/mole Effect of sunlight to break bond

C-H 420-560 No
C-Cl 320-460 Depends on constituents
C-C 300-720 Depends on constituents
Polyvinyl chloride (PVC)
Usages
 Upholstery,
 Luggage fabric,
 Wall coverings,
 Floor coverings,
 Tarpaulins,
 Shoe uppers
Polyurethane (PU)
Polyurethane(PU)
Components of polyurethane
 Polyisocyanate n(NCO-R-NCO)
 As crosslinking agents, polyisocyanates play a key role with
respect to processing, curing and the resulting coating properties
 Polyols n(HO-R’-OH)

Urethane

 If the functionalities of the reactants are three or more, branched or

cross-linked polymers are formed.
 By varying R and R’ segments of the polyaddition reaction and
other ingredients, a range of products can be formed (foam, fibers,
coating, soft and hard elastomers, flexible
Polyurethane(PU)
 Important polyisocyanates

Hexamethylene diisocyanate Isophorone diisocyanate

Diphenyl methane diisocyanate

Toluene diisocyanate
Polyurethane(PU)
 Polyisocyanates
 Aromatic isocyanates yield polyurethanes that turn
yellow with exposure to light
 Various aliphatic and cycloaliphatic diisocyanates are
used in the industry to produce polyurethanes, which do
not turn yellow upon light exposure
 The most important among the aliphatics is
hexamethylene diisocyanate (HMDI).
 It is used extensively for coating.
Polyurethane(PU)
Polyols
 The second component is polyols
 Polyester polyols

 Polyether polyols
Polyurethane(PU)
 The characteristic of polyurethane coating material
depends on the chain length of isocyanates and
polyols
 If they have short chains, the polymer will be hard
and low solubility due to hydrogen bonding between
C=O and N-H.
 If the chains are long, the polymer will be very soft
 Mostly polyurethane are prepared from three basic
ingredients
 Long chain polyols
 Isocyanates
 Chain extenders and crosslinkers
Polyurethane(PU)
 Chain extenders and crosslinkers are low molecular weight poly
functional alcohols and amines
 The difunctional amines and alcohols are chain extenders
 The compounds with functionality greater than two are cross-linkers
What are these compounds?
 Ethylene glycol, 1,4-butanediol, glycerol and trimethylol propane
 Derivatives of diaminophenylmethane and m-phenylenediamines
Polyurethane(PU)
 Catalysts
 Enhance the rate of reaction
 The most commonly used catalysts are tertiary amine
and organo tin compounds
Polyurethane(PU)
Structure –properties relationship
 Hard segments
 These are formed due to the reaction between
isocyanates and short chain diols (chain extenders and
crosslinkers)
 High polarity
 Rigid at room temperature
 Soft segments
 These are formed due to the reaction between
isocyanates and long chain diols
 Low polarity
 Soft and flexible at room temperature
Polyurethane(PU)
 Polyester polyurethanes
 Generally, show higher modulus, tensile strength, hardness
and the thermo-oxidative stability
 They also show better resistance to hydrocarbons, oils and
greases.
 But they show poor hydrolytic stability due to ester linkages

 Polyether polyurethanes
 Have better hydrolytic stability
 Poor thermo-oxidative stability
 The thermo-oxidative stability can be improved by adding
antioxidants.
 Polyether urethanes show better resistance to micro-
organisms attack.
Polyurethane(PU)
Preparation of polyurethane
Two methods are used
 One shot method
 Polymerization takes place in one step, all the ingredients
(polyisocyanates, polyols, chain extenders and crosslinkers,
catalysts) are mixed simultaneously
 The reaction is very exothermic
 Prepolymer method
 First prepolymer is prepared by reacting polyisocyanate and polyols
(Mw=20,000)
 Prepolymer can be –NCO or –OH terminated
 -NCO terminated is of great technical importance
 Then chain extenders and crosslinkers are added
Polyurethane(PU)
Coating methods of polyurethane
Two methods
 One component system
 Two component system
Polyurethane(PU)
One component system
 Reactive one component system
 Low molecular weight prepolymers with terminal
isocyanates
 Dissolved in solvent of low polarity
 After coating, they are cured in moist environment

 Completely reacted one component system

 Already prepared high molecular polymer
 Dissolved in solvents of high polarity
 No need for curing, just physical drying
Polyurethane(PU)
 Two components system
 The polyisocyanate component, usually in the form of a
solution, is mixed with the polyhydroxy component
prior to coating.
 Curing of these coatings occurs due to the formation of
urethane linkages.
 The properties of the resulting coatings depend on
various factors
 The polyol type and molecular weight
 The temperature of the reaction
 The concentration of polar groups, i.e., urethane and urea
 The cross-linking density
Polyurethane(PU)
 Additives
 Silica fillers to reduce gloss,
 UV absorbers,
 Antioxidants,
 flow improvers
The solvents used for coating should be free of moisture and
reactive hydrogen
The pigments should also be free of moisture
Polyurethane(PU)
Aqueous dispersions of PU
 Aqueous dispersions are used due to …
 Low emission of organic volatiles to meet emission
control regulations
 Lower toxicity and fire hazard
 Economy of the solvent
 Viscosity of latex independent of molecular weight
 They are prepared by mixing…….
 Polyether/polyester polyol,
 Diisocyanates,
 Polyfunctional amines
 chain extenders
Polyurethane(PU)
Preparation of emulsion
 Emulsifiers can be internal or external
 Internal emulsifier contains hydrophilic groups
incoporated into polymer chains
 Emusifiers can be ionic or nonionic
Polyurethane(PU)
Preparation of emulsion
Acetone Process
 A solution of high molecular weight polyurethane-urea ionomer is
built up (after reaction and chain extension) in a solvent like acetone
 The solution is then mixed into water
Polyurethane(PU)
Melt Dispersion Process
 A -NCO terminated prepolymer is reacted with ammonia or urea to
form urea end groups
 The reaction with urea is carried out at a high temperature ∼130 ◦ C.
 The hot melt is poured into water at an elevated temperature to form a
spontaneous dispersion.

Chain extension is
carried out by reaction
of the oligomer with
formaldehyde
Polyurethane(PU)
Aqueous dispersions of PU
 On drying of the dispersion on a substrate, the discrete polymer
particles should fuse to form a continuous organic phase with
entanglement of polymer chains.
 Poor fusion leads to poor gloss and poor physical properties of the film.
If cross-links are present, the film-forming property decreases.
 An improvement can be made by adding high boiling, water miscible
solvent in the latex. On evaporation of water, a solution of PU in the
solvent is left behind.
Polyurethane(PU)
 Problems of Aqueous PU Coatings
 Poor water and solvent resistance
 It can be overcome by….
 Grafting hydrophobic chains, usually acrylics, on the PU
backbone
 Cross-linking of the polyurethane chains

Solvent based systems always give better properties

as compared to Aqueous systems
Polyurethane(PU)
 Main features of PU coating
 Dry cleanability, as no plasticizers are used
 Low temperature flexibility
 Overall toughness—very high tensile, tear strength, and
abrasion
 Softer handle
 Can be coated to give leather-like property and
appearance
Polyurethane(PU)
 Additives
 Thickeners (polyacrylate)
 Pigments
 Flame retardants
 External crosslinking agents
Polyurethane(PU)
 Applications of PU coated fabrics
 Water proof protective clothing
 Water proof/ breathable clothing
 Aircraft life jackets
 Artificial leather products
 Functional bodywear
Polyurethane(PU)
 Mechanism of yellowing
Acrylic coating
Acrylic polymers
 The commonly used monomers are esters of acrylic
and methacrylic acid

The properties depends on R and R’

If R = H, the polymer will be tacky and soft (acrylate)

If R = CH3, the polymer will be hard and brittle

(methacrylate)
Acrylic polymers
The alcohol chain length R’ effects the Tg
Acrylic polymers
 A proper adjustment of the amount of each type of
monomer yields polymers of desirable hardness or
flexibility.
 A vast majority of commercially available acrylic
polymers are copolymers of acrylic and methacrylic
esters.
 Exceptional resistance to UV light.
 Resistance to heat, ozone, chemicals, water and dry-
cleaning solvents.
 Resistance to stiffening on ageing.
Acrylic polymers
 Acrylic Formulation
 Acrylic resin
 Thickener
 Ammonia
 Cross-linking agent
 Water
Acrylic polymers
 Usages
 acrylics are used as backcoating materials in automotive
upholstery fabric and carpets, window drapes, and pile
fabrics used for outerwear
Substrates For Coating
Substrates for coating
The parameters need to be considered
 Strength and modulus
 Creep behavior
 Resistance to acids and chemicals
 Adhesion requirement
 Resistance to microbiological attack
 Environment of use
 Durability
 Dimensional stability
 Cost
Substrates for coating
Substrate characteristics for specific End-use
 Fiber type and form such as staple, filament, etc.
 Yarn type and construction
 Fabric form, i.e., woven, nonwoven, and knitted and
their construction
Substrates for coating
 Fiber Type
 Cotton
 Moderate strength, low resiliency (wrinkles easily), excellent adhesion
 Viscose rayon
 Similar as cotton
 Polypropylene
 Poor adhesion, low weight, good strength
 Polyester
 Poor adhesion, static charges, thermal shrinkage, excellent strength
 Nylon
 High strength, elasticity, abrasion resistance, static charges, thermal
shrinkage
 Nomex
 Flame resistant, excellent strength
 Kevlar
 Ultrahigh strength and modulus.
Substrates for coating
Substrates for coating
Yarn properties depend on
 Short staple fibers
 Long staple fibers
 Filament
 Twist
Yarn type
 Spun yarn
 Strength is due to twist, hairiness enhances the
absorbancy and adhesion
 Continuous Filament Yarn
 Can be twisted or intermingled to impart strength,
texturing can be done to enhance adhesion
Substrates for coating
 Types of Fabric
 Woven
 Knitted
 Nonwoven

 Woven Fabrics
 Plain
 Twill
 Satin
Substrates for coating
 Plain Woven Fabrics
 The highest quantity of interlacings in comparison with
other weaves,
 High tensile strength
 Stiffest fabric
 Low absorbancy
Substrates for coating
 Twill Weave
 The amount of interlacing in the twill weave is less than
in a plain weave
 Fabric is thicker than Plain woven fabric
 Low interfiber friction, pliable, good wrinkle recovery
 Lower strength
Substrates for coating
 Satin
 Long floats
 High pliability, high wrinkle recovery
 High yarn slippage,
Substrates for coating
 Knitted Fabrics
 The properties of knitted fabrics are determined by
 Size of loop, linear density of yarn, type of knitting structure
 Knitted fabrics have high tear, tensile strength
 High resiliency, elasticity
Substrates for coating
 Nonwovens
 Adhesive-Bonded Fabrics
 Web is prepared on carding or similar machine
 Fibers can be oriented or at random in web
 Fabric quality depends on quality of web
 Adhesion is achieved by using adhesive or by thermoplastic
fibers
 The tenacity of fabric is around 1 to 4 cN/tex
 Spunbonded Fabrics
 Continuous filament coming out of spinnerettes is allowed to
fall on moving conveyor by using stream of air.
 Bonding be done by using adhesive or by heating if filament is
thermoplastic
 Tenacity is 5-8cN/tex
Substrates for coating
 Needlebonded (Needlepunched) Fabrics
 An array of needles is pushed through the web
 The strength of needlepunched fabrics varies in the
range of 2 to 5 cN/tex.
 Hydroentanglement
 A fine jet of water is used to push fibers from the surface
toward the interior
 Strength is approximately similar as of needlebonded
Textile Coating Methods
Coating method
 Divided into two categories depending upon the state
of coating material
 Fluid (can be solution or paste)
 Knife coaters
 Roll coaters
 Impregnators
 Spray coaters
 Dry compound (solid powder or film)
 Melt coating: extrusion coating, Powder coating
 Calendering: Thermoplastic polymers and rubber compounds
 Lamination
Coating method
 The choice of coating method depends upon….
 Nature of the substrate
 Form of the resin and viscosity of the coating fluid
 End product and accuracy of coating desired
 Economics of the process
Coating method
Main parts of coating machine
 Fabric let off
 Fabric Accumulator
 Coating head
 Drying oven
 Winding section
Fabric Accumulator
Coating method
 Classification on the basis of metering stage
 Post metering
 Process where the material is applied on the substrate and
then metered
 The excess of fluid is applied on fabric, a coating device
meters the coating to a predetermined thickness
 Commonly used method; Knife coater
 Use for noncritical weights on the substrate
Coating method
 The parameters which determine the consistancy of
coating
 Substrate tension
 Viscosity of the coating material
 Substrate uniformity and porosity
 The coating range is limited to 0.02-0.2mm
 Low investment cost and quick product changeover
Coating method
 Pre-metering
 Process where the material is metered prior to application
 The method used are roller coatings, gravure coatings, extrusion
coatings, and lamination
 The method is highly accurate and reproducible
 Coating range is 0.1-0.5mm
 Initial investment cost is high
Coating method
Knife coater
 A post-metering method
 The forward motion of fabric and
stationary blade give rotatory motion
to paste known as rolling back,
which it acts as reservoir.
 The working width of machines vary
between 1.5-4m.
 Proper control of viscosity
 Coating speed depends on solvent
Coating method
Arrangements of knife coating
 Three arrangements are commonly used
Coating method
 Floating Knife arrangement
 The knife is positioned after a support table and rests directly
on the fabric.
 The coating compound enters the interstices of the fabric due
to compressive force applied.
 This technique is good for low weight, very thin and
impermeable coatings (7-8g/m2)
 Hotair ballons and anoraks
 Factors affecting coating
 Web tension
 Viscosity
 Percent solid contents
 Specific gravity
Coating method
 knife-on-blanket arrangement

 The web is supported by endless blanket stretched

between two rollers
 The amount of coating is dependent on the tension of
the blanket, which is adjusted by the rollers.
 Good for dimensionally unstable substrates
Coating method
 knife-on-roll arrangement
 Knife is positioned on top of high precision roller. This
system is much more accurate than other knife coaters
 The gap between fabric passing over the roller and blade
determine the thickness of coating material
 The rollers can be of two types
 Steel rollers are more precise than rubber coated rollers
 Steel rollers
 Rubber coated rollers
Coating method
 Coating Knives

Knife type V type Bull nosed type Shoe type

Coating method
 Knife type Profile
 The knife is chamfered on the other side of the
rolling bank.
 The base of the knife may vary from 0.5 to 4 mm
wide.
 The sharper the base of the knife, the lower the coating
weight.
 This profile is used for lightweight coating.
Coating method
 V type profile
 knife is chamfered on both sides due to which
wedge effect is produced
 This wedge creates pressure and enhances
penetration into interstices of fabric.
Good for mechnical adhesion
 Multiple coats are applied to achieve desired results
 used for Tarpauline, hoses
Coating method
 Bull nosed type profile
 Imparts heavy coating weights with little
penetration into the weave
 Suitable for delicate fabric
Coating method
 Shoe type profile
 The front of the knife may be straight or rounded.
 The base dimension may vary from 2–30 mm.
 The toe of the blade is nearest to the substrate
 The penetration of material depends on wedge which
depends on elevation of heel
Coating method
Roll coating
 In this method coating material is first applied to roll
which touches the passing fabric and coat it
 Various arrangement are used
Coating method
Direct roll coating
 A premetered quantity of material is applied to fabric
 The quantity of material is controlled by doctor blade
 The coating thickness depends on nip pressure, coating formulation,
and absorbency of the web
 This method is also restricted to low viscosity compounds and is
suitable for coating the undersurface of the fabric
Coating method
Kiss roll coating
 It consists of pickup roll and applicator
 The pickup roll picks the coating material and is
premetered by applicator
 The coating material is applied to fabric as it touches the
roll.
 Metering is done by nip pressure

Applicator (steel)
Pickup (rubber
covered)
Coating method
Gravure coating
 Engraved roll. Coating is controled by engraved
pattern

Offset roll

Indirect gravure coater Direct gravure coater

 Suitable for extremely light weight coating

 Indirect Gravure coater good for high viscosities
 It can coat hot melt compounds
Coating method
Reverse roll coater
 Use for a wide range of viscosities and coating weights
 The accuracy of the coating is very high
 Maintain the thickness regardless of variation in
substrate thickness
Coating method
Dip coating
 Fabric is passed through the coating material and squeezed
subsequently to remove excess of material
 In dip coating, the pickup is quite low, and penetration occurs into the
interstices of the fabrics as well as in the yarns
Coating method
Transfer coating
 Direct coating has some problems
 It is applicable to closely woven, dimensionally stable
fabrics that can withstand machine tension, and it is not
suitable for excessively stretchable knitted fabrics.
 Penetration occurs in the weave of the fabric, increasing
adhesion and lowering tear strength and elongation,
resulting in a stiff fabric.
Coating method
Transfer coating
 Transfer coating solve the problem of dimensional stability, as no
tension is applied
 The most delicate and stretchable fabrics can be coated by this process
 Fabric penetration and stiffening is significantly low
Coating method
 Rotary screen coating
 Screen
 Backup roll
 Whisper blade
 Can coat upto 200g/m2
Coating method
 Strainer -extruder
Coating method
In-line lamination
 The sheet produced by calender is laminated outside
the the calender
 Good for heat sensitive substrates
Coating method
Lamination against steel belt
 For multiple sheets
Coating method
Both side coating
 Z calender
Physical Properties Of Coated Textiles
Physical Properties Of Coated Textiles
General characteristics
 Tensile strength
 Elongation
 Adhesion
 Tear resistance
 Weathering behaviour
 Microbiological degradation
 Yellowing
Physical Properties Of Coated Textiles
 Physical properties of  Coating formulation
coated fabric depend on  Coating technique
 Properties of substrate  Processing conditions
Physical Properties Of Coated Textiles
Tensile strength
 It depends on…………….
 Fiber  Actual strength of fabric
 Fineness
is always less than its
theoretical strength.
 Twist
 Theoretical strength of
 Tenacity of yarn fabric is the sum of the
 Weave tensile strength of all the
 Yarn density yarns added together
Physical Properties Of Coated Textiles
 Tensile strength of coated fabric > loomstate fabric
 Is it really so? NO!

 Because the difference of break elongation of the yarn

and the coating compound is very high

 No contribution to tensile strength by coating material

Physical Properties Of Coated Textiles
Elongation
 Coated fabrics have lesser elongation in warp direction
than loom state fabrics
 During the coating process, the fabric is subjected to
longitudinal tension, stretching the warp threads

 In weft direction, they have high elongation

 Due to the stretching of the warp threads, the looping
angle of the weft thread increases
Physical Properties Of Coated Textiles
Adhesion
 It can be of two types
 Mechnical
 Chemical
 Mechnical adhesion
 It depends on types
 Fibers
 Weave structure
Physical Properties Of Coated Textiles
Factors Affecting Adhesion
 Types of fibers
 Fiber surface, moisture, finish etc
 Construction of fabric
 Polymer for coating
 Bonding agent
 Coating method and coating conditions
Physical Properties Of Coated Textiles
Tear Strength
 It prevents the propagation of tear in coated fabric
 Factors controlling tear strength
 Construction of fabric: weave, yarn fineness, and yarn
density
 Coating material: formulation and bonding system
 Adhesion and penetration of coating material on the
textile substrate
Physical Properties Of Coated Textiles
Tear strength
 The reduction in tear strength of coated fabric with
different weave structure

Basket weave> Twill> plain

Physical Properties Of Coated Textiles
Weathering
 Weathering is combination of complex parameters in
outdoor applications
 Solar radiation
 Temperature
 Humidity and precipitation
 Wind
 Chemicals and pollutants
Physical Properties Of Coated Textiles
Weathering
 Degradation process can be one or more of following
 Volatalization of plasticizer and solvents
 Rupture of the main macromolecular chain
 Splitting of the side groups in various ways
 Formation of new groups and reactions among them
 Regional orientation—formation of crystalline regions
Physical Properties Of Coated Textiles
Mircobiological Degradation
 The plasticizers are food for microrganisms
 The prolonged exposure causes discoloration of
coating material particularly PVC.
Physical Properties Of Coated Textiles
Yellowing
 Yellowing can be due to breakage of main polymer
chain
 In polyurethane, the use of aromatic isocyanate causes
yellowing in outdoor applications
Rheology of Coating
Rheology of coating
 Rheology deals with deformation and flow of matter,
and response of matter to an applied stress.

Shear rate= γ = dv/dx

Shear stress=τ = F/A

Viscosity is ratio of shear stree to shear rate

η = τ/ γ
Rheology of coating
 Liquids where shear stress is directly proportional to
shear rate are called Newtonian

 Liquids where shear stress is not directly proportional

to shear rate are called non-Newtonian
Flow of liquids

Change in
viscosity

Newtonian Non Newtonian

system system
Shear stress rate of shear
Example is water
No change in viscosity Time independent Time dependent

Plastic flow Psedo plastic flow Dilatant flow Thixotropy Rhopexy

Bingham body Shear Shear
yeild thickening Decrease Increase in
thinning
in viscosity viscosity
with time with time
Rheology of coating
Types of non-Newtonian liquids
 Bingham body behavior
 A certain minimum stress is necessary before flow
begins. This is known as the yield value. Once the yield
value is reached, the behavior is Newtonian.
Mathematically; τ = τ0+ γη; where τ0 is yield stress

 e.g, Toothpaste
 Mayonnaise, ketchup
Rheology of coating
Types of non-Newtonian liquids
 Dilatancy And Pseudoplasticity
 In dilatant liquid, the apparent viscosity increases with shear rate,
i.e., shear stress increases with shear rate.
 The dispersed particles pile up due to shear
 Cornstarch and Water Mixture, wet sand,

 In Pseudoplastic liquids, the apparent viscosity decreases with shear

rate
 The molecules arrange themselves in such a way that it favors flow
 Yogurt, xanthan gum or carboxymethyl cellulose (CMC) solutions,
cosmetic creams and lotions
Rheology of coating
Types of non-Newtonian liquids
 Thixotropy And Rheopexy
 If the viscosity of fluid decreases with the passage of time at
constant shear rate, it is called thixotropic e.g Paints
 As the shear force is reduced, the viscosity increases but at a
lesser rate, forming a hysteresis loop. The area of the
hysteresis loop is a measure of the thixotropy of the coating.

 This behavior is good for coating. The viscosity lowers during

application
 High viscosity at low shear rate prevents sagging and dripping
Rheology of coating
 Exact opposite to Thixotropy is Rheopexy; the viscosity
increases with the passage of time at constat shear rate
Rheology of coating
Rheology of Plastisol
 Viscosity of coating paste is very important
 High viscosity may cause the uneven deposition on
fabric and may bend the coating head.
 Very dilute dispersions containing around 50%
plasticizers behave like Newtonian fluids
 Formulations having high concentrations of polymers
behave like non-Newtonian fluids
 It can be pseudoplastic, dilatant or thixotropic
depending upon formulation
Rheology of coating
 Flow properties of paste depends on
 Particles size and their distribution
 Nature of plasticizer
 Amount of plasticizer
Rheology of coating
Particle size and size distribution
 Primary particles range from 1-1.3 µm
 During spraying bigger particles are formed(40-50µm)
called secondary particles
 The paste viscosity depends on part of primary as well
as secondary particles
 Depending upon viscosity, the resins can be divided
into three categories.
 High viscosity resins: particles size<0.5µm and are
monodisperse. Secondary particles does not affect
viscosity
 Medium viscosity resin: primary particles are
polydispersed (0.8-1.5µm). Secondary particles have
some effect on viscosity.
Rheology of coating
 Low viscosity resins: they have broader particle distribution. The
secondary particle greatly affects the viscosity

Plasticizers
 The viscosity of plasticizer and its solvating power affect the
viscosity of paste (freshly prepared and aged paste)
 Higher the solvating power, higher is the viscosity
 Polar plasticizers yield high viscosity pastes
Rheology of coating
Viscosity change during Fusion
 Decrease in viscosity due to rise in temperature linked
to reduction in plasticizer viscosity (A-B)
 Increase in viscosity due to salvation leading to gelling
(B-C), the temperature at which this happens is called
gellation temperature.
 The viscosity increases with
temperature reaching it maximum
value

 Then slight decrease due to melting of microcrystal

Testing of Coated Textiles
COATING MASS PER UNIT AREA
 Bulk of coating is removed mechanically
 Remaining material is removed by refluxing in proper
solution
 After washing with acetone dried and weighed
 The process is repeated till difference between successive
refluxing, drying and weighing is less 1%.
 PU is stripped with 2N Alcoholic KOH
 Natural rubber is stripped with xylene
 PVC is stripped with methyl ethyl ketone
Testing of Coated Textiles
Degree of Fusion
 This test is specific for PVC
 The coated fabric is treated with acetone at 23 °C for 30
min
 Then, the surface is observed.
 If there is no cracking or disintegration of the coating
Testing of Coated Textiles
COATING ADHESION
 Plies are held in jaws and amount of load to separate them
is determined

ACCELERATED AGING
 The coated samples are heated in an air oven at 70 °C or 100
°C for 168h.
 The stiffening, softening, brittleness and sticking is
checked
 The physical properties are determined before and after
this test.
 For PVC coated fabric, loss of plasticizer is essentially
measured