Surface Treatment Technologies
Case Study for the IAC – January 2011
Coating and laminating
Coating and laminating processes are widely used to improve and
modify the physical properties and appearance of fabric, be it
knitted, woven or nonwoven. They have also facilitated the
development of entirely new products and have led to innovations
in the area of “smart” materials.
Coating and lamination cuts across virtually every product group in
the textile industry, including composites, where the potential is
especially broad.
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Australian capability
Australias manufacturing capability for surface treatments on fabrics is estimated to be as follows:
• 12 coaters• 7 laminators• 1 plasma• 35 stenters with padding funtionality
• There are no dedicated training programs for personnel on this machinery
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Applications for coated and laminated textiles
• Home furnishings • Protective apparel • Automotive interiors • Industrial textiles - filtration• Performance wear • Technical fabrics• Conveyor belts• Medical textiles• Agriculture textiles• Military textiles• Transport – train and aerospace• Marine textiles• Flooring
Industry Association consortium
In 2010 the TTNA commissioned the CSIRO to develop the workshop on “Surface technologies”.
Thirty industry personnel attended the workshop which was held at the Rio Tinto Innovation Centre in conjunction with the FSAA
workshop on “chemical finishes to enhance filtration properties.”
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CSIRO. Surface Technologies
Following are the course notes.......
Course Outline• Adhesion theory
• Definitions• Adhesion theory• Surface energy and spreading• Failure modes
• Types of adhesives• Classification of adhesives• Properties of adhesives
• Surface preparation• Eroding techniques• Chemical modification
• Application and test methods• Preparation, application and curing• Test methods
• Examples
The Mechanics of Adhesion - Introduction
What is an Adhesive?
• Any substance that holds materials together in a functional manner.
• Terms used to describe adhesives include:• Cement, mucilage, glue, paste
• In this workshop we will only consider organic adhesives, but inorganic substances such as Portland Cement can be considered an adhesive
Contents
• Definitions (in notes)• History of Adhesives• Adhesion Theories• Surface Energy • Failure modes• Why use Adhesives
Definitions
• Absorption• The penetration of a liquid into a solid structure by capillary action
• Adherend or Substrate• Material to be bonded by an adhesive
• Adsorption• The interaction of a liquid and solid surface without penetration
• Catalyst• Chemical that accelerates a chemical reaction such as curing• Usually at low concentration and not consumed by the reaction
Definitions
• Cure• Change the physical properties of an adhesive by chemical
reaction
• Cohesive• Resistant to failure by rupture of the material (rather than the bond)
• Creep• Deformation of a material under constant load
• Laminate• Bond together layers of adherends/substrates
• Open time• Time in which dry adhesive layers may still be bonded (contact
adhesive)
Definitions
• Pot-life• The maximum time between preparing the adhesive and its
application
• Shelf-life• the maximum storage time before use
• Shrinkage• Reduction of volume on curing
• Tack• Resistance to detach from the material surface on immediate low
pressure contact
History of Adhesives
• Up to 19th century all glues were animal or plant based• Collagen based obtained from skin, bone, sinew, fish• Starches and dextrins obtained from plants
• 20th century synthetic adhesives developed• 30’s acrylics, 70’s second generation acrylics• 80’s aqueous based systems• 90’s curable hot melts and moisture cure urethanes
4000 BC
Tree sapresins
2000 1500 1000 500 0 500 1000 1500
Animal gluerecorded
Wood glues Veneeringmarquetry
glues refinedProtein, grains
furniture1750 patent
Post-it note
Pressure sensitive acrylic foamed hot melts
Hot melt
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Synthetic polymers and resinsAcrylics, polyurethanes epoxy resins
BakelitePhenolic resins
Curable hot meltsMoisture cure urethanes
Adhesives
To form a good bond:• The adhesive must wet and spread on the surface of the
material being bonded• Generally the adhesive must harden to a cohesively strong
solid (Pressure sensitive adhesives remain liquid)• Many adhesives contain additives to improve the
performance of the adhesive• Stabilizers, plasticisers, fillers, tackifiers and coupling agents
Surface Tension, Surface Energy and Wetting
• Interactions between the molecules of a liquid and those of another insoluble liquid or gas results in the formation of an interface. Energy is required to change the form of this interface or surface.
• Surface or interfacial tension is the work required to change the shape of the interface.
• Surface tension is easily measured using a tensiometer
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Surface Energy and Contact Angle
• Three interfacial forces balance at the edge of a liquid drop on a solid surface. Two are in opposite directions and one forms the “contact angle” to the surface.
• The surface energy of a solid surface (σS) can be indirectly determined from the drop shape of liquids of known surface tension (σL )when they are placed on the solid surface. As the interfacial tension between the liquid and solid (σLS) is unknown, a single liquid cannot be used. This method is not useful for fibrous surfaces.
fLS fVS
fLV
fLV = interfacial force of drop & vapour
fLS = interfacial force of drop & solid surface
fVS = interfacial force of solid & vapour
θ L
LSS
LV
LSVS
fff
σσσθ −
=−
=cos
Contact Angle
• Bond strength depends on contact angle• Low contact angle à stronger bond
• Non-wetting liquid – θ > 90o, wetting liquid θ < 90o
θ θ
Surfaces wet when the solid surface energy is greater than the liquid surface tension
Wetting increases as the difference between the liquid surface tension and solid surface energy increases
Measurement of Surface Energy
Standard liquids
Contact angles
Apply a model
Surface energyσ = σP + σD
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ZismanFowkesOwens, Wendt, Rabel, KaelbleWuSchultzEquations of state
Measurement of Surface Energy
• Drops of liquids of known surface energy• Observe spreading behaviour
• Wilhelmy plate method• Microbalance measurement of the force on the solid as it is
immersed and retracted from the liquid• F = M + lγLcosθ – buoyancy in liquidWhere M = mass of solid plate, l = length of liquid contact, γ L = liquid
surface tension• Goniometer
• Direct measurement
Measurement of Surface Energy
• Zisman plot is the simplest method for determining the surface energy of a solid surface. The surface energy is the surface tension where the two lines intersect.
CSIRO. Surface Technologies
Cosθ
Liquid surface tension mJm-20 20 40 60
1.0
0.6
0.2
x xx
xx
x
x
x
N-decaneCyclohexane
n-tetradecanetoluene
Benzyl alcohol
Ethylene glycol
N-pentanen-hexane
Surface Free Energy – polar and disperse components
DS
DL
oSL
σσθ
σσ
≅
≥
≅
0
PTFE e.g. surfacenonpolar
PS
PL
DS
DL
SL
PS
DS
σσ
σσ
σσσσ
>
≤
>≈==
or )7.5 ,3.32(PMA e.g.
surfacesPolar The contact angle depends on the polarity of the surface and probe liquids
Units in table mJm-2
Surface liquid Surface tension
Dispersive component
Polar component
Contactangle
PTFE n-decane 23.8 23.8 0 42.3
PTFE n-tetradecane 26.4 26.4 0 49.4
PTFE toluene 28.4 26.1 2.3 58.2
PMA nitromethane 36.5 22 14.5 16.5
PMA methyl benzoate 37.2 27 10.2 3.9
PMA benzyl alcohol 39 30.3 8.7 15.1
Measurement of Surface Energy
• Owens, Wendt, Rabel, Kaelble model gives both the surface energy and polar and disperse components of the surface energy.
y=mx+b
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)(2 )(2 ))cos( (1 PL
PS
DS γγγγγθ +=+ D
LLV
DSD
L
PLP
SDL
L σσ
σσ
σθσ
+=+
2)1(cos
DL
L
σθσ
2)1(cos +
DL
PL
σ
σ
DSσ
PSσ
Measurement of Surface Energy of Fabrics
• Balance methodBalance
LIQUID
FABRIC
W
time
δW
• Water Uptake Rate – comparative • Saturation level - comparative• δW = force due to surface tension – need to know perimeter precisely
Spreading Pressure
• Spreading Pressure• πe = γS - γSV
• γS = solid surface free energy, γSV = solid/vapour surface free energy
• S (spreading parameter) = γSG - γSL - γL• Must be negative for liquid to spread
Spreading Pressures
Liquid γL (mJm-2) Solid θ (o) πe (mJm-2)
Hexane 17.9 PTFE 12 3.28
Octane 21.1 PTFE 26 4.9
Water 72.8 PE 94 0
Methyleneiodide 50.8 PE 52 0
Hexadecane 27.2 PE 0 7.6
Hexane 17.9 PE 0 14.5
Surface energy PTFE 19.1 mJm-2, PE 33.2 mJm-2
Theories of Adhesion
• Mechanical Interlocking• Adhesive wets the surface, entering irregularities in the surface
before curing• Physical Adsorption
• Van der Waals forces across the interface between the adhesive and substrate
• Chemical Bonding• Chemical bonds (covalent, ionic, hydrogen) form across the
interface• Diffusion
• Interdiffusion of polymers in contact so the boundary is removed• Electrostatic
• Electrical double layer formed when two metals are placed in contact
Mechanical Interlocking
• Adhesive enters irregularities in the surface before hardening
• requires good wetting and flow properties in the adhesive• Surface roughness increases the apparent contact angle
• A very rough surface at the micron scale does not wet well• Keys into the surface to form a strong bond
• Similar action to hooks and loops in Velcro• Most common mechanism in textiles
• Interfacing using hot melt adhesive• Latex back on carpets
• Adhesive usually below Tg during use• Adhesive has glass like properties over the normal operating
temperature range
Poor wetting
Good wetting
Mechanical Interlocking
Glass surface viewed by AFM. Roughness height approximately 50nm.
Adhesive
Good wetting and flow into the surface roughness à good adhesion.
Physical Adsorption
• Van der Waals forces across the interface• Interaction of dipoles in the surfaces
• Atoms of different electronegativity in a molecule induce a non-uniform distribution of charge in the molecule called a dipole
• Adhesive must wet the surface as the forces only act over a short range (<1nm)
• Only top layer of the surface is involved• Surface energy of the adhesive and substrates are used to assess
adhesion• Three types of dipole interaction with decreasing strength
• Permanent dipole – permanent dipole• Water between glass
• Permanent dipole – induced dipole• Epoxy and polyethylene
• Instantaneous dipole (non-polar molecules)• Cling wrap – polyethylene film
Stre
ngth
Adhesion• Work of adhesion
• Where σ1 = surface free energy of substrate 1, σ2 = surface free energy of substrate 2 and σ12 = surface free energy of the interface between substrate 1 and 2. σ12 is minimised to give maximum bond strength.
• Polar/disperse mismatched
• Polar/disperse matched
INNNNNNNNNI
NIIIIIIIIIN
)(2
)(2
2121
21212112
1221
PPDDA
PPDD
A
W
W
σσσσ
σσσσσσσ
σσσ
+=∴
+−+=
−+=
nN/m40 nN/m,10 nN/m,5020mN.m 80mN/m,
nN/m10 nN/m,40 nN/m,50
222
12
111
===
=====
DPA
DP
Wσσσ
σσσσ
nN/m40 nN/m,10 nN/m,500mN.m 100mN/m,
nN/m40 nN/m,10 nN/m,50
222
12
111
===
=====
DPA
DP
Wσσσ
σσσσ
1
2
I I I IN NIII
Example - Gecko
• Gecko foot• Covered in hairs• Each hair splits into hundreds of spatula shaped ends• Van der Waals attraction between hairs and surface• Changing the hair to surface angle by curling the toe allows easy
removal and walking
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Photo by Bjørn Christian Tørrissen (Wikipedia)
Chemical Bonding
• Formation of ionic, covalent or hydrogen bonds• Ionic – metal epoxy, some pressure sensitive adhesives
• water -dispersible sulfopolyester• Some easily disrupted by water
• Covalent – silicones, BAP on wool• Permanent strong bond
• Hydrogen – postage stamps (PVA to cellulose)• Easily debonded by water, humidity sensitive
• Stronger bonds than adsorption• Often requires a coupling agent or surface treatment
• Coupling agents are compounds that contain two reactive groups, one that bonds to the substrate and the other to the surface coating
Diffusion
• Interdiffusion of polymers in contact• Boundary between adherends is eventually removed• Requires mobile polymer chains (T>Tg)• Requires compatibility between polymers
• Same polymer• Polyethylene and polypropylene are not compatible
• Solvent welding of polymers• Used in wetsuit manufacture, contact adhesives
Electrostatic
• Electron transfer from one material to another at interface• Development of electrical double layer at interface (opposite
charges in materials)• Attraction between materials
• May be applicable to some metals• Most polymers are insulators
Weak Boundary Layer
• Presence of contaminants leads to a weak bond• Contaminants include processing oils, softeners, waxes• Oxides on metals can result in weak bonds
• Some adhesive designed to dissolve contaminants• Acrylics can dissolve some oilsà stronger bonds
Glass Transition Temperature• Temperature where polymer changes from glassy solid to a rubber• Mechanical properties radically change at Tg
• Below Tg limited translational and rotational movement of polymer backbone• Above Tg movement of backbone
• Polar groups increase Tg
• Non-polar groups decrease Tg
• Adding liquids to the adhesive lowers TgPolymer Abbreviation Tg (°C)Polymethacrylic acid PMAA 228
Poly(methyl methacrylate) PMMA 105
Poly (ethyl methacrylate) PEMA 65
Poly(n-propyl methacrylate) PPMA 35
Poly(n-butyl methacrylate) PBMA 20
Polychloroprene CR -50
Polyisoprene (natural rubber) rubber -75
Polydimethylsiloxane PDMS -127
Measurement of Glass Transition Temperature
• DSC
• Change in properties at Tg.• Rapid increase in temperature• Reduced stiffness
Sample Reference
Heaters
Tg Temperature à
Hea
t Flo
w à
Tg
RubberyGlassy
Temperature à
Vol
ume à
Tg
Glassy
Temperature à
Mod
ulus
à Rubbery
Glass Transition Temperature
It is unacceptable for an adhesive or surface coating to pass through the glass transition during service
Failure Modes
• Adhesive and adherend must be compatible• 5 elements to consider• Weakest element determines the joint strength
Adherend 1 Adherend 2Adhesive
Interface 1 Interface 2
Failure modes
• Failure of bond or material
Adhesive failure
Cohesive failure
Advantages of Adhesive Bonding
• Able to bond materials that would otherwise be difficult to join
• Thin sheet materials, laminates, fibres, paper products, carpets• Stress is distributed over a wider area• Dissimilar materials can be joined• Fabrication of complex shapes• Improved appearance• Reduced cost• Rapid assembly• Good sealing and insulating properties• Improved product performance
Disadvantages of Adhesive Bonding
• Need for surface preparation• Relatively long curing times
• Optimum strength develops over time• Joint design important
• Need to understand stresses applied to the bond• Temperature limitations
• Thermal and mechanical shock• Poor electrical and thermal conductivity• Degradation• Dismantling may be difficult
• New adhesives improve disassembly e.g. hot melt adhesives• Creep• Retooling costs
Why use Adhesives
• Adhesives may be the only solution to a bonding problem• Large area to be joined (e.g. bench tops), membrane fabrics
• Improved performance• Upholstery fabrics, plywood
• Join dissimilar materials• Wet suits (neoprene to nylon)
• Join heat sensitive materials• Thermoplastic components
• Laminated structures• Laminated fabrics
• Reinforced structures• Fibreglass, tyres
• Temporary fastening• Labels, ‘sticky tape’, ‘post-it notes’
Adhesive Materials – Properties and Selection
Contents
• Types of Adhesives• Structural adhesives• Pressure sensitive adhesives • Contact adhesives• Hot-melt adhesives• Reactive hot melt adhesives• Drying adhesives – solvent and water• UV cure adhesives
• Properties of Selected Adhesive• Selection of Bond Type and Adhesives
Classification of Adhesives
• Thermoplastic• Melt without degrading
• Thermoset• Heat curing• Chemical reaction• Catalysed
• Structural adhesives• Pressure sensitive adhesives • Contact adhesives• Hot-melt adhesives• Drying adhesives – solvent and water
Structural Adhesives
• Requirements• Good load carrying capacity• Long-term durability• Resistance to:
• Heat, Solvents, Fatigue
• Adhesive families• Epoxies, polyurethanes, acrylics, surface activated acrylics,
cyanoacrylates, silicones
Advantages DisadvantagesHigh strength Surfaces must be matched
Bond dissimilar materials Clean surfaces
Large surface area Max temperature 100oC
Distribute load Weather resistance
No weakening of bonded parts Design requirements
Where usedComposite materialsConstructionCarpet
Pressure sensitive adhesives
• Permanently tacky adhesives• Balance between adhesion and cohesion• Polar adhesives for high surface energy surfaces• Relatively low MW• Low Tg, often < ambient (rubber like)
• Requires pressure to achieve good bond• Low viscosity à better wetting at low pressure
• Adhesive often carried between a backing and release liner• PSA’s include natural and synthetic rubbers (SBR),
thermoplastic elastomers, polyacrylates, polyvinylalkyl ethers, and silicones.
PSA’s
Property Rubber Based Acrylic SiliconeCost Low Moderate HighTack High Low-high LowPeel Strength Mod-high Low-high Low-modService Temp 0 To 65oc -40 To 150oc -73 To 250ocEnvironment Indoor Indoor/Outdoor Indoor/OutdoorUV Resistance Poor Excellent ExcellentSolvent/Chem. Resistance
Poor Good Excellent
Plasticiser Resistance
Poor Poor-fair Good
Bond To High Energy Surface
Excellent Excellent Excellent
Bond To Low Energy Surface
Moderate Poor-high High
• Adhesive selection
PSA’s
Advantages DisadvantagesRemovable? Release liner
Invisible bonding Aging
Reduced weight PSA manufacture - solvents
Range of bond strengths and properties
Non-permanent bond
No open time Low sheer and peel strength
Can bond dissimilar materials Temperature sensitive
Contact adhesives• Similar to PSA• Semi-structural adhesives
• Sheer strength > 1000 kPa• Peel strength > 3kg/cm length
• Adhesive applied to both surfaces and solvent allowed to evaporate before joining pieces
• Diffusion mechanism involved as adhesive on each component diffuses across the interface. The rheology immediately before bonding is important for good bonding
• Usually based on solvent solutions of neoprene• -(CH2-C(Cl)=CH-CH2)- polychloroprene or poly-2-chlorobutadiene• Also polyurethanes, SBR, acrylic polymers
• Water dispersion versions replacing solvent systems• Reduced strength and durability
http://www.veganwares.com/factory.htm
Contact Adhesives
Advantages DisadvantagesNo mixing required Cannot be repositionedImmediate green strength Use of solventsStronger than PSA Open time
Water based systems have long drying times
Hot Melt Adhesives
• Thermoplastic resins• Ethylene vinyl acetate (EVA), polyamides, polyester, acrylics
• Applied as hot liquids• Application temperature 150-200oC• Must flow and wet surface• Solid at 80oC with amorphous and crystalline domains• Preheating of the surface to control cooling rate
• Limited by upper operating temperature – approximately 65oC
• Applications• Book binding, veneer coating, laminated textiles, labels, packaging,
construction
Hot Melt Adhesives
Property Ethylene Vinyl Acetate
Polyamide Polyester Polyethylene
Softening point 40°C 100°C 60 -200°C
Melting point 95°C 195-220°C 267°C 137°C
Crystallinity Low Low High Low or High
Melt flow index 6 2 5 5
Tensile strength MPa
18 13 31 13
Elongation, % 800 300 500 150
Cost Low to Mod Moderate High Low
Typical properties of hot melt adhesives
Melt flow index is the ease of flow of the molten adhesive
Hot Melt Adhesives
Advantages DisadvantagesNo solvents Poor temperature resistance
No mixing required Creep Immediate green strength Water and solvent permeation
Easy handling, several formats High viscosity
Reactive Hot Melt Adhesives
• Thermoplastic adhesives that react after application to become a thermosetting polymer
• Polyurethanes, silane modified urethanes, acrylates (UV), silicones• Moisture cure polyurethane most common
• Others include UV cure acrylates and silicones• Overcome many of the disadvantages of hot melts
• Higher operating temperatures - >100oC• Improved environment stability – humidity, chemical
• Able to apply at lower temperature – 65oC• Applications
• Automotive components, laminated textiles, carpet manufacture
Reactive Hot Melt Adhesives
Advantages Disadvantages
Lower application temperature Higher cost
Improved temperature resistance Full cure in several days
Improved adhesion Short open time
Improved creep resistance Moisture sensitive in applicator
Tough and flexible Special applicators needed
Applicator clean-up
Drying adhesives
Types of drying adhesives and common uses• Loss of organic solvent
• Contact adhesives• Loss of water
• Pastes of starch derivatives or PVA adhesives• Water moistenable
• Poly(vinyl alcohol) PVOH and poly(vinyl acetate)• Aqueous emulsions
• Latex e.g. PVA, acrylic
UV Cured Adhesives
• Cure on exposure to UV radiation• Very rapid cure possible
• Usually a low molecular weight prepolymer and initiator dissolved in monomer
• Photoinitiator produces radicals that begin polymerisation• Often large volume decrease on curing
• Reduced by use of particulate fillers• Must be visible to UV source
Adhesive Formulations
• Adhesives are usually not pure polymers• Formulations include
• Adhesive polymer• Fillers
• Improve the properties of the liquid and cured adhesive e.g. increase viscosity of liquid and shear strength of solid epoxy
• Examples: zinc oxide, titanium oxide, silica, clay, pigments• Tackifiers
• Added to increase the tack of the adhesive• Examples: rosin esters, polyterpene resins, hydrocarbons
• Plasticizers• Added to soften the cured adhesive – “make more plastic”• Examples: mineral oil, lanolin, lecithin, glycol
• Antioxidants• Inhibits oxidation of the adhesive, increases shelf and service life• Examples: metal chelating agents, common antioxidants
Selection of Adhesives
• Factors to consider when selecting adhesives• Surfaces to be bonded• Material properties
• Maximum operating temperature• Thermal and moisture expansion
• Joint design• Rate of stress load, total stress load and direction stress is applied to
the joint• Area of joint
• Cure time• Hot melt < drying < chemical reaction
• Open time• Creep• Flexibility• Peel strength
Selection of Adhesives
• Factors to consider when selecting adhesives• Application method• Process speed • Further processing – e.g. finishing operations• Service conditions
• Weathering • Washability, dry-clean• Temperature range• need for autoclaving
• Ability to disassemble goods for recycling
Selection of Adhesives
MaterialAdhesive
NR CR PU Si PU foam
PVC foam
PTFE PE Glass
Acrylic X X X X * X ** X **Cyanoacrylate *** *** ** X * * ** * X
Epoxy ** ** X X * * X X **Chloroprene *** *** ** X ** *** * X X
Urethane ** X *** X ** * X X **Silicone X X X *** X X * * *SBR X X X X * *** X X X
Nitrile rubber *** X *** X ** *** ** *** *
• Selection guide
NR – nitrile rubber, CR – polychloroprene rubber, PU – polyurethane, PVC – polyvinyl chloride, PTFE – poly tetrafluoroethylene, PE – polyethylene, SBR – styrene butadiene rubberX – not recommended, * - poor, ** - fair, *** - good
Surface Analysis
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Surface Analysis
• Contact Angle (see above)• FT-IR Spectroscopy • X-ray Photoelectron Spectroscopy• Scanning Probe Microscopy
Fourier Transform –Infra Red Spectroscopy
• Attenuated Total Reflectance (ATR)• 2 micron penetration into surface by effervescent wave. Therefore
provides information about the surface chemistry.• Requires smooth surface and close contact with the crystal.
Multiple bounce crystals give better signals with fabrics.• Permanent dipole in the bond required to absorb IR radiation and
give a signal
• Chemical information about surface• Chemical bonding• Chemical groups• Oxidation states
Sample
ATR crystal
IR beam
FT-IR
• Other surface sensitive techniques• Grazing angle spectroscopy• Specular reflectance• Photoacoustic spectroscopy• Diffuse reflectance
microphone
PhotoacousticGrazing angle
Specular and diffusereflectance
X-ray Photoelectron Spectroscopy (XPS)
• Also called Electron Spectroscopy for Chemical Analysis (ESCA)
• High vacuum technique• Sample is irradiated with a monochromatic X-ray beam• Electrons with characteristic energy are ejected from atoms in the
surface
Bvcrist, Wikipedia
XPS Binding Energies
Element Binding energyEb (eV)
Relative sensitivity
Core level
C 285 0.25 IsO 530 0.66 1sF 690 1.0 1sNa 1072 2.3 1sSi 102 0.27 2p
• Energy of emitted electron (Ek) is unique to atom and oxidation state
Ek = hv – Eb – ψwhere hv = energy of x-ray, Eb = binding energy of electron,
ψ = work function of spectrometer (constant)
XPS
• Surface technique only• Electrons from <10nm below the surface• Reducing the angle can increase surface sensitivity
• Static Secondary Ion Mass Spectroscopy (SSIM)• Related technique
• High energy ion beam used to sputter material from surface• Mass spectrometer to analyse ions produced• Very surface specific – 1nm
Scanning Probe Microscopy
• Scanning Probe Microscopy (SPM or AFM)• Three modes of operation• Force-distance (non-contact) mode
• Tip of the cantilever maintains constant distance from sample surface• Distance determined by force on tip
• Contact mode• The tip is in contact with the surface at constant force
• Tapping mode• Tip is osculated near the surface and changes in deflection observed
• Able to determine some chemical information using functional tips
Surface Modification
Contents: Surface Modification Technologies
• Abrasion• Solvents• Coupling agents• Corona• Low Pressure Plasma• Atmospheric plasma• Flame
Abrasion
• Increase surface roughness and removes contaminants through mechanical means
• Increases surface area of contact• So increases adhesion strength
• Usually used on hard surfaces• Sand paper, emery paper, wet & dry• Shot blast, bead blast
Cleaning & Degreasing
• Solvents are often used to clean and degrease the surfaces before adhesion.
• They are very good at gross level cleaning • BUT: as little as 1g/m2 of contamination, e.g. a monolayer,
can affect adhesion unless the adhesive can absorb the contamination.
• 1g/m2 contamination is the residue of 0.1L/m2 of liquid containing 10ppm non-volatiles e.g. from a dirty container.
• Also many plastics and fibres contain additives designed to bloom at the surface
Cleaning & Degreasing
• Metals: • Trichloroethylene• N-propyl bromide
• Polycarbonates: • Methanol• isopropanol• detergent
• Fluorocarbons: • Trichloroethylene
• Polyesters: • Detergent, • Acetone, MEK
• Polyethylene: • Acetone,• MEK
• Polypropylene: • Acetone, • MEK
• Polystyrene: • Methanol, • Isopropanol, • detergent
• Polyurethane:• Acetone, • MEK
Commonly Used Degreasing Solvents
Wet Chemical Treatments
• Metals: • Various acidic etches
• Fluorocarbons e.g. PTFE: • 1% Sodium in ammonia; or epoxy primer & heat 10min at 370oC
plus 5min at 400oC• Polyesters:
• 20% Sodium Hydroxide at 95oC 10mins• Polyethylene, Polypropylene:
• Sodium dichromate + water + Sulphuric acid (93%) in proportions 5:8:100
Coupling Agents
• Adhesion promotors can be reactive (or nonreactive), if they contain a functional group that can react with a functional group on the substrates
• Coupling Agents• the term coupling agent is used if one of the components is an
inorganic component (filler, metal etc). • Reactive coupling agents will contain reactive groups.
• Reactive groups can be Carboxylic acid groups, Epoxy groups (e.g. glycidylmethacrylate, oxazoline), Maleic anhydride, or others.
• Non reactive coupling agents draw their functionality mainly from their polarity. They then represent an intermediate polarity between the adhering substrates and the adhesive. Adhesion is usually by Van der Waals forces.
Corona & Plasma Treatments
• Corona is the most common form of atmospheric pressure plasma
• It is a dielectric barrier discharge plasma (DBD) most commonly used on plastic films for printing and adhesion enhancement
• Higher treatment levels are obtained with other forms of plasmas, including low, medium and atmospheric pressure plasmas in a variety of process gases
ELECTRODES
DIELECTRIC BARRIER
CORONA or PLASMA
High Voltage AC
“STATIONARY” MICRODISCHARGES
What is a Plasma?
TAKE A GAS
ADD ENERGY
AS
HEAT
LIGHT
ELECTRICITY
IONS
ELECTRONS
ATOMS
IONISE THE GAS
Two Temperatures
Hot & Cold Plasmas
Electron temp
Ion & atom temp
>>>
Examples of Plasmas
Fluorescent light
Cool plasma
Hot, high pressure
Thermonuclear device
Welding arc
LighteningCool, low pressure
Xenon sputtering plasma
Hot, atmospheric pressure
Sun - Hot, high pressure (inside)
History
• Low Pressure Plasmas- vacuum, batch process • Effects & benefits well proven but it is industrially difficult to use
• Dielectric Barrier Discharge, “Corona” • less effective but industrially robust
• NEW Systems: Atmospheric Pressure, highly effective, industrially robust:
• Some commercial systems are available, many under development
Plasma cutter
Textile treatment with permission Textile World 2008,
Dielectric Barrier Discharge
Breakdown initiates Micro-filament forms
Electron concentrationElectron concentration
Corona Systems
• Discharge between ceramic coated HV electrodes and grounded steel rollers.
• Problem: micro-discharges recur in same spots:• Breakdown occurs at ions from last cycle• Leads to poor uniformity• Low concentration of reactive species• Relatively low surface energy modification
Dielectric Barrier Discharge
• For an effective surface treatment we need: • random distribution of micro-filaments
• To achieve:• Uniformity of treatment and • Maximise the concentration of reactive species
CORONA GLOW-LIKE
Glow-like Discharge
Advantages• Uniform plasma• Low temperature but very reactive• Generates free oxygen (at the fibre surface)• Penetrates permeable fabrics
Electrodes
Dielectric barrier
Plasma
High Voltage AC
Uniform plasma
Gas >
Design considerationsGas composition & flowElectrode designVoltage & frequency
Fibre
Plasma Surface Treatments & CoatingsFree radicals
UV photons
PlasmaElectric field
Produce reactive groups on fibre surface
e.g. Carbonyl, carboxylic acid, hydroxyl groups
Oxidise surface
UV & Ions cross-link surface molecules
Plasma Surface Treatment
Optimum Result:• UV Crosslinked layer covalently bonded to the adhesive
via plasma produced reactive groups. • Cross-linked layer:
• strong • stabilises the surface against reorientation and diffusion of low
molecular weight material from the bulk
Crosslinked layer
Bulk Polymer
Covalent Bonding
Adhesive
Enhance bonding
Enable printing
Increase or decrease wettability
Apply Functional Polymers
Monomer gas
Polymerisation& Grafting
Monomer gas
e.g. Fluoro-polymers
Addition of a monomer gas to the plasma produces a highly crosslinked polymer on the surface.
Surface Modification and Polymerisation
The surface can be tailored for the application. e.g.
• Surface energy can be raised for bonding, printing, hydrophilicity
• Surface energy can be lowered by grafting polymers either in the plasma or post plasma treatment for stain-blocking, cake release, increased hydrophobicity
Example: PE
Surface tension increase after plasma treatment (arbitrary units)
PE Fabric
untreated 1 sec 5 sec 10 sec 5 sec ( 4 days later)
1 0.03 0.25 0.37 0.34 0.29
2 0.07 0.25 0.3 0.30 0.33
3 0.11 0.29 0.29 0.3 0.31
Low and Medium Pressure Plasmas
• Consist of Vacuum vessels, pumping systems, RF drivers• Batch process, and expensive• Good control of the environment• Highly uniform plasma over large volume• Can use dangerous chemicals safely• Medium pressure plasmas can have quicker pump down
and cheaper pumping systems
www.europlasma.be
Low and Medium Pressure Plasmas
• High energy surfaces reorientate over time so that the reactive groups bury themselves into the bulk polymer
• Better control of process gases, less oxygen, may allow control of the competition between cross linking and oxidation.
• Cross-linked surface layer resists reorientation and is stronger
Industrial Plasmas
• Saturated treatment in 2 seconds• At 20m / min:
• Need a treatment length of ~ 0.7m
• Process can be in-line with other processes:• Printing• Laminating• Stenter• Coater
Optimum Treatments
• Each polymer & adhesive system requires optimization of the energy density and plasma chemistry.
• Under treatment leaves contamination, which may result in poor adhesion
• Over treatment can produce a layer of low molecular weight material – wettable and appears to have the right chemistry but is weakly bonded to bulk.
Flame Treatment
Courtesy, Eddie Grant, Aerogen
Flame Treatment
• Treatment level depends on the substrate, the time spent in the flame and the temperature and chemistry of the flame.
• Excess treatment results in flame-polishing, which can be useful but doesn’t enhance adhesion.
Courtesy, Eddie Grant, Aerogen
Flame Chemistry
• The most reactive species are not in the hottest part of the flame
• Small reactive species such as H , OH and O have higher concentrations near the tip of the flame
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H2OCO2O2OH2OHO
R∙
COOH2OH
Temperature scaleLow high
Air Fuel
Flame Treatment• Flame Treatment can be more stable than Corona
treatment on polypropylene but Corona is more user friendly. Plasma treatments can give higher surface energies but lower stability but the plateau level is still usually higher than Corona or Flame.
Courtesy, Eddie Grant, Aerogen
Flame Treatment
• Gas Mixture: Fuel/Air Ratio
• The excess O2 level in the flame is critical to the surface energy enhancement attained.
Courtesy, Eddie Grant, Aerogen
Flame Treatment
Critical Parameters• Combustion conditions –
• Air / Gas ratio• The burner to substrate gap• The dwell time of the substrate
in the flame• The substrate• Mechanical handling• Flame energy
Courtesy Aerogen
Flame Treatment
• A water cooled backing roller is often used to dissipate the heat of the flame.
• The roller also controls the position of lightweight films and webs
Courtesy Aerogen
Aerogen Control System
Courtesy Aerogen
Measurement of Surface Modification
• Indirect Tests: • Surface energy, surface tension, contact angle, wicking test
• Chemical Composition • XPS, NMR, FTIR etc
• Direct tests: • adhesion, peel tests, bond strength
Summary
• Properties of plasma processes:• low energy (~10kW / m2 )• low effluent• high speed• cheap, reliable, efficient • inexpensive• replace solvents (environmental and/or OHS hazards)
• Properties of flame treatment:• high speed• more stable surface
• Properties imparted to fibres:• increased fibre surface energy• no reduction in strength• enhanced bonding• greater wettability• greater reactivity
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Adhesive Materials – Application Methods for Textiles
Contents
• Spraying• Roll Coating• Knife Coating• Printing• Hot Melt• Foam• Powder• Release Coatings
Spraying
• Advantages:• Suitable for large areas and uneven surfaces• Good control of adhesive film thickness• Requires low viscosity solutions
• Disadvantages:• Overspray• Use of solvents• Aerosol generation
• Small areas can be applied using a hand spray• Very good for fabrics
• (Video of spray application)• http://www.youtube.com/watch?v=jw1DTpUqFeU
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Roll Coating
• Direct roll and Gravure roll
Gap between the rollers determines add-on
• Kiss roll
Fabric and roller at different speeds and direction
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• Doctor roll
Fabric and roller in same direction
• Reverse roll
Metering roller to control add-on
Knife Coating
• Knife over air Knife over roll
Thinner coating possible Gap determines thickness
• Knife over belt or table Blade shapes
Over air or surface options sharp, rounded, Jdetermines penetration and add-on.
• http://www.youtube.com/watch?v=LusEXygxUoo
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Curtain Coating
• Falling curtain of adhesive coats material• Very even coating possible• Only adhesive touched the substrate
• Useful for delicate substrates
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http://www.youtube.com/watch?v=UquzkUUqqwo
Printing
• Rotary screen printing• Non-continuous application possible• Control of add-on• Improved flexibility of textile• Surface application possible• Tensionless application
Hot Melt
• Large surface area Powder applicators• Roller coating• Doctor blade• Printing
• Small area• Glue gun
• Powder• Scatter• Electrostatic• Paste• Engraved roller
Foam
• Doctor blade• Slot • Reduces water usage
• Parabolic foam applicator head• Constant foam age• Eliminates head tracking effects
Release coatings
• Used on PSA tapes• Low surface energy coating
• Coating on liner has good adhesion to the liner but poor adhesion to adhesive on substrate
• Mould release agents• Needs good cohesion – must separate cleanly• Silicones most common release agent
• Bond to liner by mechanical interlocking• Release energy can be tailored to the application
AdhesiveTight releaseSubstrate
LinerAdhesive
Tight releaseEasy release
SummaryCoating method
Viscosity cP
Coating weightg/m2
Coating accuracy
%
Coating speedm/min
Adhesive types
Wire rod 100-1,000 15-100 10 100-150 Solution, emulsion
Knife over roll
4,000-50,000 25-750 10 100-400 Solution, emulsion, 100% solids
Reverse roll 300-50,000 25-250 5 100-700 Solution, emulsion
Gravure 15-1500 2-50 2 100-700 Solution, emulsion
Extrusion die
400-500,000 15-750 5 300-700 Emulsion, hot melt, 100% solids
Slot die 400-200,000 20-700 2 100-300 Emulsion, hot melt, 100% solids
curtain 50,000-125,000 20-500 2 100-500 Emulsion, hot melt
Viscosity of water at 20oC is 1cP, honey is 2,000-10,000cP
Adhesive Materials – Bonding in Textiles
Contents
• Coatings• Shoes• Laminates• Carpets• Non-wovens• Automotive
Examples of the use of adhesives
Fabric to foam flocks
non-wovens
Case Study – Coated Blind Fabric
• Typical blind fabric has several layers of resin. For a typical ‘blackout blind’ these are:
1. A stiff resin impregnated into the fabric to give the desired bending properties
2. A softer, usually white layer to protect the visual appearance of the fabric
3. A soft layer containing a black pigment – the blackout layer4. A soft, usually white layer, to improve the back appearance.
• Resins are usually acrylics with different Tg (glass transition temperature)
• A final layer may be applied to enhance the visual appearance of the product – e.g. a flock
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http://blinds247.net/rollers_holland_blinds.html
Case Study - shoe
1.Fully supported Box-Toe for shape retention 2.Cotton Vamp Lining 3.Heavy Gauge Upper 4.Double eyestay Construction 5.Padded tongue6.Runner's Ortho Cup7.Foam padded collar8.Brushed suede Counter Insert9.Triad Heel10.Special Shock Retention Heel & Sole Design 11.Special Rubber Blended Sole12.High Density Foam Insole 13.Texon Insoles14.Comfort lining 15.Fore-part Pad & Flex Zone 16.Chevron Design Sole
Shoe
• Adhesive requirements• Flexibility• Elongation• Moisture resistance• (chemical resistance)• Dissimilar materials – urethane/SBR to leather, cotton to leather• Fast tack• High green strength• Cure conditions – room temperature, elevated temperatures• Low fatigue
Shoe
• Inner Sole to Upper• Polychloroprene (neoprene) contact cement
• Outer Sole to Upper• Traditional cement – contact adhesive (neoprene)• Urethanes and polyamides now also used• Some manufacturers cast the urethane sole on the inner sole
• Toe cap• Urethane contact cement• Trend to aqueous contact cement systems
• Sports shoes• Tend to hot melt polyamide
Laminated Films
• One substrate coated then nipped to a second substrate• Wet lamination
• Water based solutions or emulsions• Natural products e.g. starch, dextrin• Synthetic polymers e.g. polyvinyl acetate, acrylics• Reduced VOC
• 100% reactive liquids• Polyurethanes, polyesters
• Solvent based adhesives• Reduced drying time and energy• Potential environmental concerns – VOC emissions
• Conventional coating equipment• One substrate must be porous
Laminated Films
• Dry lamination• Hot melt adhesives e.g. ethylene vinyl acetate copolymers• Liquid adhesives partially dried before lamination e.g. acrylic
emulsions, silicones• 100% reactive solids e.g. polyurethanes, UV curable acrylates• Application methods include powder application
• Green strength important for handling of laminate• Full strength usually 24 hours• Coating method and adhesive depend on substrate
characteristics• Surface preparation• Sensitivity to moisture, solvents• Temperature stability
Laminated Films
• Adhesives• Other functional properties may be included – e.g. flame resistance• Consider gas permeability, optical clarity, thermoforming capability,
electrical properties, chemical and heat resistance• Resistance to tunnelling – local delamination caused by substrates
of different extensibilities• Adhesive properties – adhesion, cohesion, flow, flexibility• Water borne adhesives becoming more popular, improving in
properties - acrylics and polyurethanes• UV cure adhesives
Example – Gore-Tex
• The simplest rain wear is a two layer sandwich. The outer layer is typically nylon or polyester and provides strength. The inner one is polyurethane that provides water resistance at the cost of breathability.
• Early Gore-Tex fabric replaced the inner layer of PU with a thin, porous fluoropolymer membrane (Teflon) coating that is bonded to a fabric.
• However the exposed Teflon membrane layer was easily damaged. A third, PU layer, was added as the inner of the "protection" layers. Then either a loose fabric shell layer, or a bonded coating is added to the garment to protect the membrane sandwich.
CSIRO. Surface Technologies
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http://www.youtube.com/watch?v=X5IgcmKXb8o
Non-woven
Thermal Mechanical ChemicalCalendering
PointOverall
EntanglementNeedle punchSpunlace
Emulsion adhesiveButadiene copolymersVinyl acetateVinyl chloride
Air oven Perforation Solvent bondingRadiant heat Pressure embossing Thermoplastic dry
bondingUltrasonic Stitching Powder resinFlame Hot melt bondingExtrusion
• Many ways to bond non-woven fibres
Latex Bonding of Non-wovens
• Non-woven strength function of fibre, binder and adhesion strength
• Good cohesion requires coalescence of latex droplets• Increase surface energy• Decrease particle size
• Adhesion to fibres• Latex and polymer must wet fibres• Surfactants added to reduce latex surface tension• Size added to fibre to improve wetting• Web density affects binder performance
Good bonding
Poor bonding
Latex Bonding of Non-wovens
Advantages Disadvantages
Low viscosity, easy to apply Entrainment of surfactant
Wide range of binders High temperature to dry
Easy to handle Polymer migration
Simple application machinery Environmental concerns -surfactants
No solvent, low VOC
Carpet production
• Move from conventional latex production
• Latex integrated into tufts• Difficult to separate• Generally non-recyclable
• to recyclable products• Thermoplastic adhesives• Easier separation for recycling by
heating
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Images from http://www.shawcontractgroup.com/Html/PerformanceBackings
Case Study - AutomotiveComponent Adhesive use %Headliners 33Sound insulation 17Door and side panels 10Carpet bonding 14Dashboard assemblies 8Seat upholstery 8Other 10
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