Adhesion - Considerations, Testing And Interpretation
NREL PV Module Reliability Workshop (Feb 24, 2015)Adhesion - Considerations, Testing and Interpretation3MRenewable Energy DivisionPresenterScott R. Meyer: Senior Specialist-Product and Application Development Engineer;3M headquarters in St. Paul, MN, USA; Chemical Engineer B.S. degree from Iowa State University, 1985; 28 years at 3M Company in various divisions; experience with PSAtapes, epoxies, urethanes and fluoroelastomers; 20 years of Experience with Adhesives; 6 years of tapes and adhesives experience related to the solar industry. 3M2013. All rights reserved.
Topics:1. Adhesion and Testing Failure ModesTypes of ForcesTypes of testing2. Material & Adhesive Characteristics Perform differently – Difficult to compare materials3. Many Variables Impact Test Results and Performance Material typesTime & TemperatureEnvironmentalAging (outside scope of this discussion)4. Rigid PV Module Application 2Relevant Forces & Testing7 March 3M 2015. All Rights Reserved.
Why is Adhesion Important In PV Modules?Many Adhesion Areas in a Module Can FailBulk (with-in a material)Frame Each material has its own bulk characteristics Some materials (e.g. Backsheets, EPEs) have layers within thematerial that may have additional Interfacial adhesion issues aswell as different bulk characteristicsInterfaces Front Glass to EncapsulantEncapsulant to Cells and RibbonsEncapsulant to Backsheet or Backside GlassJ.Box to BacksheetRails to Backsheets or Backside GlassFrames to Backsheets or Backside Glass Back SideGlass of PVEdge Seals – Glass/Glass Thin FilmModuleTape or Liquid Adh.Hat Channel Metal Rail37 March 3M 2015. All Rights Reserved.
Adhesion Molecular attraction that holds material together (Single material or multiple layers) Does it stick together? Is it resistant to de-bonding?Modes of Failure (De-bonding) Cohesive Failure (CO) – Bulk layer Adhesion Failure (AF) - Interface between layersIs CO failure required or is ahigh force to failure sufficient?Not Always easy to identify failure mode Mixed failure modes (Some CO & some AF) Thin bulk layer surface failure (Can be difficult to see)47 March 3M 2015. All Rights Reserved.
Can Be Difficult To Say If Cohesive (CO) or Adhesion (AF) Failure Some TimesDynamic Tensile/PluckPSA Foam TapeThinCohesive90 PeelLiq. SiliconeCohesive Not To Hard -But Some May Say Mostly AFBut Really Thin CO Film 5Difficult – Most would Say Mostly Mixed with35% CO and 65% AF to GlassBut Really CO – 35% CO & 65% Thin CO Film7 March 3M 2015. All Rights Reserved.
Types of Forces3. Cleavage2. Tensile/Pluck1. ShearTensile Forceapplied to an edgeShearForce𝑆𝑡𝑟𝑒𝑠𝑠 𝐹𝑜𝑟𝑐𝑒/𝐴𝑟𝑒𝑎Force isParallel toBond areaShearForceTensileForce𝑆𝑡𝑟𝑒𝑠𝑠 𝐹𝑜𝑟𝑐𝑒/𝐴𝑟𝑒𝑎Force isPerpendicularto Bond area 𝐹𝑜𝑟𝑐𝑒/𝑊𝑖𝑑𝑡ℎ 𝐸𝑛𝑒𝑟𝑔𝑦/𝐴𝑟𝑒𝑎Fracture MechanicsFracture Energy to propagate a crackTensileForceTensile Force appliedperpendicular to an edgeAreaAreaForce6More complex to understandwhat cleavage results mean.7 March 3M 2015. All Rights Reserved.
Force Applied In Different Test Modesa. Constant Rate - Displacement (or Force)b. Constant - Force (or Displacement)Rate Constant distance/time (mm/min)Constant force (kg)c. Cyclic – Displacement or Force goes up and downForce oscillates with time77 March 3M 2015. All Rights Reserved.
Constant Rate Displacement Lab Test ExamplesT Block Tensile/pluckOverlap ShearPeelStatic Overlap Shear87 March 3M 2015. All Rights Reserved.
Comments on Peel Testing Peel is a special class of a cleavage test Easy to run Complex with regards to understanding what it means relative to performance in anapplication; Fracture Energy Many variables impact results – Difficult to compare materials unless identical: Configurations of Peel Test (e.g. 90 ,180 ,T-Peel, various fixtures, .) Pull speed (Rate) Temperature Humidity Dwell time Adhesive (Material Characteristics, thickness) Substrates (Material Characteristics, thickness) Backing (Material Characteristics, thickness) - Can have large ImpactWilliams and Kauzlaurich, Strain, 47(5), 439-448, 2011 𝐺 𝑎 𝑃/𝑏 (1 𝜀 𝑎 cos 𝜃 ) ℎ 0 𝜀 𝑎 𝜎 𝑑𝜀 𝐺 𝑑𝑏fractureenergy9Total work doneEnergy used to Energy dissipatedstretch peeling in plastic bendingarm materialof peeling arm7 March 3M 2015. All Rights Reserved.
Effect of Backing Thickness in Conventional Peel TestTotal peel force/ portion due tofracture energyPeelWilliams and Kauzlaurich, Strain, 47(5), 439-448, 2011Peel can be 50% higherdue to backing effects Same adhesiveSame backing except thicknessBacking thickness range:75 to 350 µm107 March 3M 2015. All Rights Reserved.
Comments on Peel Testing (Continued) Peel may not be the best test to use to simulate the forces of PV module applications Be cautious in the interpretation of peel data; conclusions can be misleadingOnly thing worse than no data is “bad” or misleading data !When to use peel:111.Understanding the impact of dwell on adhesion build – How much time should you give somethingto reach its best interfacial adhesion?2.QC tests during manufacturing of an adhesive or identical construction - Are things changing?3.If application is in a peel mode7 March 3M 2015. All Rights Reserved.
Example Of Constant Load Lab TestsOne Condition Pass/Fail Measure Displacement as a f(time).Multiple Conditions Constant Force To Rupture (CFTR) Failure Analysis Creates projections on expected failure pointTime Temperature SuperpositionCan be Done in Shear or TensileStatic Overlap Shear127 March 3M 2015. All Rights Reserved.
Adhesive TypesAdhesive State Changes – During Bonding§ Curing Liquids― forms bond in liquid (unreacted) state; Crosslinks during cure― e.g. epoxies, reactive polyurethanes― Some may become glassy (e.g. structural epoxy & acrylics)§ Hot Melt Adhesives (thermoplastics)― melt crystals to form bond; solidifies on cooling to give strength― Can have crosslinking (e.g. encapsulants)― e.g. polyamides, thermoplastic polyurethanes, polyolefinsNo Change in Adhesive State – During Bonding§ Pressure Sensitive Adhesives (PSA)― forms bond with contact time and pressure― relies on viscoelasticity to provide resistance to debonding137 March 3M 2015. All Rights Reserved.
Many Variables Impact Adhesion Performance Environmental Aging No ChangeCrosslinkingDegradation (Breaking Molecular Bonds) Dwell Time Time to each optimal performance - Surface wet out & chemical reactionsBe careful, Dwell can cause issues when comparing if not allowed to reach optimal performance Adhesive, Substrate, & Backing Bulk CharacteristicsSurface ChemistryThickness Rate and Temperature 14Different for different material classes7 March 3M 2015. All Rights Reserved.
Adhesive and Substrate PropertiesStiffness Dependence on Temperature for Polymers Stiffness is impacted by Temperature Stiffness is also impacted by Rate (Speed)Tm examples:SiliconesAcrylic PSAPET (oriented)EVA (40%-9%)GlassAmorphousAmorphous260’C50’C to Tg examples:CrosslinkedSilicones -100’CAcrylic PSA-40’C to 0’CPET (oriented)70’C to 90’CEpoxies70 to 250’CGlass (non polymeric) 500’CAmorphousGlasstransitionTg15Crystal melting pointTemperatureIncreasingcrosslinkdensityTm7 March 3M 2015. All Rights Reserved.
Temperature & Test Rate - Significant Impact On An Adhesive Some material are influenced more by this than others .e.g.silicone versus acrylic PSA Need to ask what is important in the applicationEffect of Rate on Adhesive StrengthEffect of Temperature on Adh. StrengthTechnique that can be used to relate time & temperature– time temperature super-positioning (hot is like slow; cold is like fast) à Master curve167 March 3M 2015. All Rights Reserved.
Typical Rate & Temperature Impact On Peeluncrosslinkedadhesionfailure (AF)SmoothPeelLog r*a(T)Hot and/or slowCold and/or fastTime &/or TempCO failure if peel force exceedsbacking, substrate, or adhesivestrength.Log(F/(bT)ShockyPeelPeel ForceCO failure if peel force exceedsbacking, substrate, or adhesivestrength.Log(F/(bT)Peel Forcecrosslinkedcohesivedisentanglement ofchainsShockyPeeladhesionfailure (AF)SmoothPeelLog r*a(T)Hot and/or slowCold and/or fastTime &/or TempWhat is the temperature and rate that should be used to represent the application?177 March 3M 2015. All Rights Reserved.
Time Temperature Super-postitioning Shear CFTR ExampleTime and temperature dependence - failure times in constant shear load of 2204 foam tapeTime-temperature superpositionSAFT 2204 Constant Force to Rupture Failure1000000SAFT 2204 Master Curve - 23C reference temperature1,000,000 Minutes 1.9 years10,000,000 Minutes 19 years10000000100,000 Minutes 70 days10000023 CTime to failure/shift factor(T) (minutes)Time to failure (minutes)1000010001001010.11000001000023 C90 C10001001010.10.0100.20.40.60.8Stress (MPa)18log shift factor at 90C -2.1Same curve shape at 90C as at 23Cbut everything happens 126 timesfaster (10 2.1) at 90’C100000090 C11.21.40.0100.20.40.60.811.21.4Stress (MPa)7 March 3M 2015. All Rights Reserved.
Time Temperature Super-posititioning – When It Doesn’t WorkWhen does time-temperature superposition not work?§ Semi-crystalline materials― Not work with materials that are Crystalline - melting of crystal phase produces softeningthat will not be seen below Tm regardless of time scale of test§ Multi-phase materials― different phases have different sensitivity to temperature§ Temperature causes irreversible changes/degradation of material197 March 3M 2015. All Rights Reserved.
Each Application is Unique - Need to ask the followingØ What are the critical forces that can cause failure? Type - Shear, Tensile, Cleavage Mode - Constant Load, Constant Rate, cyclic Limit - maximum forces requirementØ What are reasonable tests that can be run to help get a perspective on performance? Usually have to make compromises to do the best you can on a small scale Need to validate &/or correlation with field results207 March 3M 2015. All Rights Reserved.
What are the type of forces on this adhesive?PV Example - Rail Bonding Adhesives In Rigid PV Modules21What are test methods that simulate the forces? Fast Tensile/Pluck Fast Shear Constant Load ShearTape or Liquid Adh.7 March 3M 2015. All Rights Reserved.
Example of Forces on Rail Bonding Adhesives In Rigid PV Modules GravityPanel Weight – Above Ambient TemperaturesLong time Scale – 25 yearsSnow Load – Cold TemperaturesWhat are the type of forces on this adhesive?θFshear W * cos θFcompressionWeightWhat are test methods thatsimulate the forces?22(Building codes use 3 second wind gusts)What are the type of forces on this adhesive?Shear & PluckShear &CompressionFshear Wind GustsShear &CompressionFshearFtensileWind gust ForceWhat are test methods thatsimulate the forces?Shear & Pluck7 March 3M 2015. All Rights Reserved.
Mechanical Load Test - IEC & UL StandardStep 1: 2400 Pa applied to front side – Hold 1 HourCompressionStep 2: 2400 Pa applied to back side – Hold 1 HourTensile/PluckConcerns 1 hr load is not representative of a wind gust. Building codes – 3 second wind GustsRepeat steps 1 & 2 three times.If want heavy snow load approval, replacelast front loading with 5400 Pa.23 Not representative of snow load becausetesting: Does not include shear Is done at room temperature7 March 3M 2015. All Rights Reserved.
Solar Panel Stack Up – Adhesion Areas in a ModuleWhat are the forces actingon the layers in the module?Gravity, Wind, CTEMismatches, installationInterfacial Front Glass to EncapsulantEncapsulant to Cells and RibbonsFrameEncapsulant to Backsheet or Backside GlassJ.Box to BacksheetRails to Backsheets or Backside GlassFrames to Backsheets or Backside GlassEdge Seals – Glass/Glass Thin FilmBulk Each material has its own bulk characteristics Some materials (e.g. Backsheets, EPEs) have layerswithin the material that may have additional Interfacialadhesion issues as well as different bulk characteristicsWhat are test methods that canbe used to simulate forces?24Shear, Tensile,CleavageBack SideGlass of PVModuleTape or Liquid Adh.Hat Channel Metal Rail7 March 3M 2015. All Rights Reserved.
Key Points:1. Peel Easy to run but complex with regards to understanding what it means relative to performance inan application. Influenced by many variables. (Backing, substrate, angle, stretching, ) May not be the best test to use to simulate the forces of PV module applications2. Understand application stresses & simulate stress as best as possible to get most relevantinformation.3. Various adh. & materials perform differently - makes it difficult to compare application performance.257 March 3M 2015. All Rights Reserved.
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Backup Slides277 March 3M 2015. All Rights Reserved.
Time & Temperature Have A Significant Impact Failure Modetransition from cohesive tointerfacial failurePeeling PET film from rubber at different rates and temperaturesGent and Petrich, Proc. Roy. Soci. A., 310, 433 (1969)cohesivePeelForcetransition from smoothto shocky peelIf peel force exceedsbacking, substrate, oradhesive strength, itcould tear and neverreach a shock PeelHot and/or slow28Cold and/or fast7 March 3M 2015. All Rights Reserved.
Substrate Type Can Have A Significant Impact Failure ModeInteraction of interfacial forces and material propertiescohesivefailureClean peelshift due to substrateShockyCold and/or fast29Rate and temperaturedependence comes fromrheological properties of theadhesive and backing7 March 3M 2015. All Rights Reserved.
7 March arm material of peeling arm energy Comments on Peel Testing Williams and Kauzlaurich, Strain, 47(5), 439-448, 2011 Peel is a special class of a cleavage test Easy to run Complex with regards to understanding what it means relative to performance in an
Adhesion Test . ASTM-4541 Pull -off Adhesion . ASTM- D3359 Dry Adhesion . Minimum average 30 events rating of . 1200 PSI on 1.5 mil profile surface . Adhesion rating (steel) 4B; adhesion rating . ASTM- D3359 Wet Adhesion . Scribed area rating (steel) 3A after 24 hours at ambient; Chip Resistance . SAE-J400 . NLT 5B . Accelerated corrosion
requirement is adhesion testing of the system in accordance with ATSM D3359 Methods A and B, “Standard Test Methods for Measuring Adhesion by Tape Test”. The primary test for coating adhesion is the cross-hatch tape adhesion method described in ASTM D3359 Method B. Applic
Pull-Off Adhesion Tester Elcometer 506 new TC. 6 www.elcometer.com Adhesion Elcometer 506 Pull-Off Adhesion Tester Testing coatings on low bond strength substrates . T50623797 Magnetic Anchor Clamp - holds actuator securely during tests on vertical surfaces T99912906 Araldite Standard Two Part Epoxy Adhesive, 2 x 15ml Tubes
cell adhesion molecules (CAMs) participate and play key roles in the inflammatory reaction [5]. The upregulation of selectins, intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) greatly increase leucocyte and inflammatory cell adhesion on the endothelium. In brief, selectins function as initiators of leucocyte
J. L. VOSSEN 122 Discussion 131 Hardness and Adhesion of Filmed Structures as Determined by the Scratch Technique--J. AHN, K. L. MITTAL, AND R. H. MACQUEEN Discussion 134 156 Threshold Adhesion Failure: An Approach to Thin-Film Adhesion Measurement Using the Stylus Method-- J
metal films. The most used adhesion metals are Ti and Cr, but the advantages of the individual materials as adhesion layers are poorly understood. The simplified adhesion layer model usually used in the micro an
The surface topography [27] of these materials and their adhesion to soft PDMS [28] has been extensively char-acterized in prior publications. The present investigation examines their adhesion to a hard material: ruby. Many adhesion studies have used atomic force m
Contego received a perfect score - Zero loss or 100% adhesion. "You can't get better than that." -Tony Scott, VP of Contego Using the ASTM D4541 standard, Contego offers 631 psi of pull test adhesion. The closest competitor shows half the adhesion Contego has, while most had one-third to one-fifteenth of Contego's strength.
