Case Study - Surface Technologies Course Notes 2010

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.

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

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

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.”

CSIRO. Surface Technologies

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

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

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 19

th

_{century all glues were animal or plant based}

• Collagen based obtained from skin, bone, sinew, fish • Starches and dextrins obtained from plants

• 20

th

_{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 sap resins 2000 1500 1000 500 0 500 1000 1500 Animal glue recorded

Wood glues Veneering

marquetry glues refined Protein, grains furniture 1750 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 resins

Acrylics, polyurethanes epoxy resins Bakelite

Phenolic resins

Curable hot melts

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

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

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 (σ

_S

) can be indirectly

determined from the drop shape of liquids of known surface

tension (σ

_L

)when they are placed on the solid surface. As the

interfacial tension between the liquid and solid (σ

_LS

) is

unknown, a single liquid cannot be used. This method is not

useful for fibrous surfaces.

f_LS f_VS

f_LV

f_LV = interfacial force of drop & vapour

f_LS = interfacial force of drop & solid surface

f_VS = interfacial force of solid & vapour

q L LS S LV LS VS

f

f

f

s

s

s

q

=

-

=

-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 energy

σ = σ

_P

+ σ

_D

CSIRO. Surface Technologies

Zisman

Fowkes

Owens, Wendt, Rabel, Kaelble

Wu

Schultz

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 + lg_Lcosθ – buoyancy in liquid

Where M = mass of solid plate, l = length of liquid contact, g _L = liquid surface tension

• Goniometer

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-2

0 20 40 60 1.0 0.6 0.2 x x x x x x x x N-decane Cyclohexane n-tetradecane toluene Benzyl alcohol Ethylene glycol N-pentane n-hexane

Surface Free Energy – polar and disperse

components

D S D L o S L

s

s

q

s

s

@ ³ @ 0 PTFE e.g. surface nonpolar P S P L D S D L S L P S D S

s

s

s

s

s

s

s

s

> £ > » = = or ) 7 . 5 , 3 . 32 ( PMA e.g. surfaces Polar

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 Contact angle 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=m

x

+

b

CSIRO. Surface Technologies

) ( 2 ) ( 2 )) cos( (1+

q

g

_LV =

g

_SD

g

_LD +

g

_SP

g

_LP D S D L P L P S D L L

s

s

s

s

s

q

s

+

₌

₊

2

)

1

(cos

D L L s q s 2 ) 1 (cos + D L P L s s D S s P S s

Measurement of Surface Energy of Fabrics

• Balance method

Balance

LIQUID

FABRIC

W

time

dW

• Water Uptake Rate – comparative • Saturation level - comparative

Spreading Pressure

• Spreading Pressure

•

p

_e

= γ

_S

- γ

_SV

• g_S = solid surface free energy, g_SV = solid/vapour surface free energy

• S (spreading parameter) = γ

_SG

- γ

_SL

- γ

_L • Must be negative for liquid to spread

Spreading Pressures

Liquid g_L (mJm-2_{) Solid} θ (o₎ π e (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

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 T

_g

during use

• Adhesive has glass like properties over the normal operating temperature range

Poor 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

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

I

NNNNNNNNN

I

N

IIIIIIIII

N

)

(

2

)

(

2

2 1 2 1 2 1 2 1 2 1 12 12 2 1 P P D D A P P D D A

W

W

s

s

s

s

s

s

s

s

s

s

s

s

s

s

+

=

\

+

-+

=

-+

=

nN/m 40 nN/m, 10 nN/m, 50 20mN.m 80mN/m, nN/m 10 nN/m, 40 nN/m, 50 2 2 2 12 1 1 1 = = = = = = = = D P A D P W s s s s s s s nN/m 40 nN/m, 10 nN/m, 50 0mN.m 100mN/m, nN/m 40 nN/m, 10 nN/m, 50 2 2 2 12 1 1 1 = = = = = = = = D P A D P W s s s s s s s 1 2

I

I

I

N

I

I

I

_N

I

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

CSIRO. Surface Technologies

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

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

Glass Transition Temperature

• Temperature where polymer changes from glassy solid to a rubber

• Mechanical properties radically change at T

_g

• Below T_g limited translational and rotational movement of polymer backbone

• Above T_g movement of backbone

• Polar groups increase T

_g

• Non-polar groups decrease T

_g

• Adding liquids to the adhesive lowers T

_g

Polymer Abbreviation T_g (°_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 T

_g

.

• Rapid increase in temperature • Reduced stiffness Sample Reference Heaters Tg Temperature à Heat Flow à Tg Rubbery Glassy Temperature à Volume à Tg Glassy Temperature à Modulus 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 Adhesive Adherend 2 Interface 1 Interface 2

Failure modes

• Failure of bond or material

Adhesive 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

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

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

Classification of Adhesives

• Thermoplastic

• Melt without degrading

• Thermoset

• Heat curing

• Chemical reaction • Catalysed

• Structural adhesives

• Pressure sensitive adhesives

• Contact adhesives

• Hot-melt adhesives

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

Disadvantages

High strength Surfaces must be matched

Bond dissimilar materials Clean surfaces

Large surface area Max temperature 100o_C

Distribute load Weather resistance

No weakening of bonded parts Design requirements

Where used

Composite materials Construction

Pressure sensitive adhesives

• Permanently tacky adhesives

• Balance between adhesion and cohesion

• Polar adhesives for high surface energy surfaces • Relatively low MW

• Low T_g, 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 Silicone

Cost Low Moderate High

Tack High Low-high Low

Peel Strength Mod-high Low-high Low-mod

Service Temp 0 To 65o_{c -40 To 150}o_{c -73 To 250}o_c

Environment Indoor Indoor/Outdoor Indoor/Outdoor

UV Resistance Poor Excellent Excellent

Solvent/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

PSA’s

Advantages

Disadvantages

Removable? 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

Contact Adhesives

Advantages

Disadvantages

No mixing required Cannot be repositioned Immediate green strength Use of solvents

Stronger 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 150-200o_C

• Must flow and wet surface

• Solid at 80o_{C with amorphous and crystalline domains}

• Preheating of the surface to control cooling rate

• Limited by upper operating temperature – approximately

65

o

_C

• 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

Hot Melt Adhesives

Advantages Disadvantages

No 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 - >100o_C

• Improved environment stability – humidity, chemical

• Able to apply at lower temperature – 65

o

_C

• Applications

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

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

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

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

Selection of Adhesives

Material Adhesive 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 rubber X – not recommended, * - poor, ** - fair, *** - good

Surface Analysis

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 Photoacoustic Grazing angle

Specular and diffuse reflectance

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

XPS Binding Energies

Element

Binding

energy

E

_b

(eV)

Relative

sensitivity

Core level

C

285

0.25

Is

O

530

0.66

1s

F

690

1.0

1s

Na

1072

2.3

1s

Si

102

0.27

2p

• Energy of emitted electron (E

_k

) is unique to atom and

oxidation state

E

_k

=

hv – E

_b

– ψ

where hv = energy of x-ray, E

_b

= 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

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

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/m

2

_{of contamination, e.g. a monolayer,}

can affect adhesion unless the adhesive can absorb the

contamination.

• 1g/m

2

_{contamination is the residue of 0.1L/m}

2

_{of liquid}

containing 10ppm non-volatiles e.g. from a dirty container.

• Also many plastics and fibres contain additives designed

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

Wet Chemical Treatments

• Metals:

• Various acidic etches

• Fluorocarbons e.g. PTFE:

• 1% Sodium in ammonia; or epoxy primer & heat 10min at 370o_C

plus 5min at 400o_C

• Polyesters:

• 20% Sodium Hydroxide at 95o_{C 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

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

Lightening

Cool, low pressure

Xenon sputtering plasma

Hot, atmospheric pressure

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

Dielectric Barrier Discharge

Breakdown initiates

Micro-filament forms

Electron concentration Electron 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

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

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 considerations

Gas composition & flow Electrode design

Fibre

Plasma Surface Treatments & Coatings

Free radicals UV photons Plasma Electric 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

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

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

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

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

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.

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

CSIRO. Surface Technologies

H₂O CO2 O₂ OH₂ OH O R∙ CO OH2 OH Temperature scale Low 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.

Flame Treatment

• Gas Mixture:

Fuel/Air Ratio

• The excess O

₂

level in

the flame is critical to

the surface energy

enhancement

attained.

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

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

Aerogen Control System

Measurement of Surface Modification

• Indirect Tests:

• Surface energy, surface tension, contact angle, wicking test

• Chemical Composition

• XPS, NMR, FTIR etc

• Direct tests:

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

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)

Roll Coating

• Direct roll and Gravure roll

Gap between the rollers determines add-on

• Kiss roll

Fabric and roller at different

speeds and direction

CSIRO. Surface Technologies

• Doctor roll

Fabric and roller in same

direction

• Reverse roll

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, J

determines penetration and add-on.

• http://www.youtube.com/watch?v=LusEXygxUoo

Curtain Coating

• Falling curtain of adhesive coats material

• Very even coating possible

• Only adhesive touched the substrate

CSIRO. Surface Technologies

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

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

Adhesive Tight release Substrate Liner Adhesive Tight release Easy release

Summary

Coating method Viscosity cP Coating weight g/m2 Coating accuracy % Coating speed m/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

Contents

• Coatings

• Shoes

• Laminates

• Carpets

• Non-wovens

• Automotive

Examples of the use of adhesives

Fabric to foam

flocks

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 layer 4. A soft, usually white layer, to improve the back appearance.

• Resins are usually acrylics with different T

_g

(glass

transition temperature)

• A final layer may be applied to enhance the visual

appearance of the product – e.g. a flock

CSIRO. Surface Technologies

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 tongue

6.Runner's Ortho Cup 7.Foam padded collar

8.Brushed suede Counter Insert 9.Triad Heel

10.Special Shock Retention Heel & Sole Design 11.Special Rubber Blended Sole

12.High Density Foam Insole 13.Texon Insoles

14.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

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

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

Non-woven

Thermal

Mechanical

Chemical

Calendering Point Overall Entanglement Needle punch Spunlace Emulsion adhesive Butadiene copolymers Vinyl acetate Vinyl chloride

Air oven Perforation Solvent bonding

Radiant heat Pressure embossing Thermoplastic dry

bonding

Ultrasonic Stitching Powder resin

Flame Hot melt bonding

Extrusion

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

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

CSIRO. Surface Technologies

Case Study - Automotive

Component

Adhesive use %

Headliners 33

Sound insulation 17

Door and side panels 10

Carpet bonding 14

Dashboard assemblies 8

Seat upholstery 8