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Wann und warum klebt Gummi-Wann klebt es nicht.
DKG – Nord: Herbsttagung 2012“Gummi klebt, Hamburg lebt”H&R Ölwerke Schindler GmbH
Dr. Hans-Joachim Graf
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Dr. Hans-Joachim Graf 2
Wann und warum klebt Gummi?- wann klebt es nicht?
➨ Introduction➨ Principles of Adhesion
● What can we learn from Nature?● Which forces are enable Adhesion
➨ What makes rubber sticky● Examples
➨ What the hint to stickiness of rubber● Examples
➨ Conclusion / summary
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Dr. Hans-Joachim Graf 3
Adhesives for broken pottery ~6000 years ago
Tar like glue (for ivory) ~6000 years ago
Animal glue (tombs – Aegypt) ~3500 – 3000 years ago
First reference in literature for making animal glue ~ 2200 years back
Animal glue for wood marquetries, fish glues, egg white to glue gold leaf,Natural ingredients for glues developed like:blood, bones, hide, milk, cheese, vegetables and grains
~2000-1500
Bows (Genghis Khan) from laminated lemmon wood and bullhorn, but formula ist lost!!
~ 1000 years ago
First factory for animal glue in NL ~ 1000 years ago
First Glue Patent GB – Fish Glue) 1750
Adhesives industrialized from NR, fish, bones, starch, milk protein After 1750
Phenolic Resin (after invention of Bakelite) ~1910
Introduction:Adhesives History
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Dr. Hans-Joachim Graf 4
➨ 1763 P.I. Macquer and L.A.M. Herissaut discovered the solubility of caoutchuc in ether and benzene. After evaporation of the solvent, the rubber hold itsproperties as before.Macquer spread rubber solutions on wax mold and made rubber hoses and shoes (1765)
➨ 1783 The British physicist J.A.C. Charles impregnated textiles with this solution, which was used to manufacture the first Hot Air Balloon of the brothers Montgolfiere.
Introduction:Adhesives History Source: Internet
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Dr. Hans-Joachim Graf 5
➨ Vulcanization (Goodyear, Hankok) 1840➨ Rubber – Fabric (Macintosh) 1823➨ Ebonite - Compound (Rollers) Late 1800➨ Brass plating (Tire Steel Cord) Since 1900➨ Phenolic Resin (C.H. Meyer) 1902➨ Phenol-Formaldehyde (Textil) 1930➨ Isocyanate Adhesive 1945➨ Chemlok 220/205 (Hughson/Lord) 1956
Structure of Phenolic ResinSource ChiUZ. 3/2010
Introduction:Adhesives History
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Dr. Hans-Joachim Graf 6
Principles of Adhesion
➨The three principles of adhesion
● Contact● Reaction● Diffusion
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Dr. Hans-Joachim Graf 7
Principles of Adhesion
➨The three principles of adhesion
● Contact● Reaction● Diffusion
Adhesion on the boundary surface in contact Bond length
[nm]Bond energy[kJ/mol]
Molecular interactions
Van der Waals forces
0,4 – 0,5 2 – 15
Hydrogen Bridges
0,2 20 – 30
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 8
➨Criteria for intimate wetting➨ Surface must be free of foreign particles. Weak layer or
contaminants (H2O, organic vapor, nitrates, ketones, alcohols, amines) has to be removed.
● A large interfacial area of intimate contact● Thermodynamically, a high surface-energy surface is the most conductive
to good wetting, particularly if adhesive contains polar functional group.● Surface energy of the adherent (reinforcement substrate) should
be greater than surface energy of the adhesive (matrix top coat).● Creation or addition of chemical groups in the adhesive● Variation in surface topography (mechanical interlocking)
Influencing parameters
Surface chemistrySurface topographyMechanical properties
Principles of Adhesion
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Dr. Hans-Joachim Graf 9
Principles of AdhesionWhat can wie from natur?
➨ In nature bonding is the most dominant joining technology
➨ Adhesives found in nature● More powerful than any
known synthetic glue – especially in the presence of water.
“Firmly Stuck” Barnacles
Source: CEN
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Gecko–like adhesives
mm
µm
nm
Pictures by K. Autum, Lewis & Clark College (Portland Oregon, USA) and S. Gorb, MPI für Metallforschung, Stuttgart, Germany
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Dr. Hans-Joachim Graf 11
Forces create Adhesion
➨ Adsorption theory● Ordinary Van der Waals forces can be responsible for adhesive strength, if
sufficiently intimate contact is achieved● Hydrogen bonding can enhance adhesion
The attraction only due to dispersion forces: Theoretical: 100 MPa !! Experimental: Strength of most joints much
smaller
Why● Air voids, cracks, geometric defects acting as stress raisers, when the joint
is loaded.● Impurities like water, organic vapor, nitrates, ketones, alcohol, and amines
can weaken adhesion.
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Dr. Hans-Joachim Graf 12
Principles of Adhesion
➨The three principles of adhesion
● Contact● Reaction● Diffusion
-X-
-X-
-X-
-X-
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 13
Principles of Adhesion
Bond length[nm]
Bond energy[kJ/mol]
Chemical Bond
Covalent 0,1 – 0,2 150 – 950
Metallic 0,3 - 0,4 100 – 400
Ionic 0,2 – 0,3 400 – 800
➨The three principles of adhesion ● Contact● Reaction● Diffusion
-X-
-X-
-X-
-X-
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 14
Principles of Adhesion
➨The three principles of adhesion ● Contact● Reaction● Diffusion
➨ Precondition for Reactions in betweenthe surfaces:
● Intimate contact● Cleanliness!!
■ No foreign material■ Functional groups■ Weak hydrogen (in case of peroxide)
● Absence of radical chain transfer / deactivation groups
-X-
-X-
-X-
-X-
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 15
Chain segments get in Interaction with a solid surface Rubber - metal Rubber, crystalline synthetic material
Side valency strengths determine the adsorption enthalpy (warmth) - Dipoles and induced dipoles - Hydrogen bridge relationships (Polarizability)
Solid
Solid
Introduction of functional groups - Chemical or physical - Pretreatment of the solid area - Chemical modification of the polymer
Roughness of the solid surface
X- X- X- X- X- X-
Y-
Y-
Y-
Y-
Y- Y- Y-
Source: Schuster, DIK
Principles of Adhesion
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Dr. Hans-Joachim Graf 16
Prinziples of Adhesion
➨The three principles of adhesion
● Contact● Reaction● Diffusion
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 17
Principles of Adhesion
Wetting Diffusion
Source: Metten; Thesis 2002
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Dr. Hans-Joachim Graf 18
Principles of Adhesion
Inter diffusion of different polymeric chains
Thermodynamic Compatibility
Molecular dynamics, Chain mobility
Process parameter P, T
Bond strength
Entanglement of chains in the Boundary layer (mechanical adhesion)
Influence of parameters on diffusion
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 19
Principles of Adhesion
➨The three principles of adhesion ● Contact● Reaction● Diffusion
Bond length[nm]
Bond energy[kJ/mol]
Chemical Bond
Covalent 0,1 – 0,2 150 – 950Molecular interactions
Van der Waals forces
0,4 – 0,5 2 – 15
Hydrogen Bridges
0,2 20 – 30
Forces:- A little bit of everything!- But in a broader layer!
Source: Schuster, DIK
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Dr. Hans-Joachim Graf 20
Example 1: Rubber to metal
Source: DOW
Metal surface treatedSurface Energy ~> 72 dyne/cm -O
H
-OH
-OH
-OH
-OH
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Dr. Hans-Joachim Graf 21
Example 1: Rubber to metal
Source: DOW
Metal surface treatedSurface Energy ~> 72 dyne/cm(Hydrophilic)
-OH
-OH
-OH
-OH
-OH
Primer
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Dr. Hans-Joachim Graf 22
Example 1: Rubber to metal
Source: DOW
Metal surface treatedSurface Energy ~> 72 dyne/cm(Hydrophilic)
-OH
-OH
-OH
-OH
-OH
Primer
Chlorinated Rubbers+CrosslinkerTop Coat
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Dr. Hans-Joachim Graf 23
Example 1: Rubber to metal
Source: DOW
Metal surface treatedSurface Energy ~> 72 dyne/cm(Hydrophilic)
-OH
-OH
-OH
-OH
-OH
Primer
Chlorinated Rubbers+CrosslinkerTop Coat
NBR / NR / EPDM CompoundRubber
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Dr. Hans-Joachim Graf 24
Example 1: Rubber to metal
Source: DOW
Metal surface treatedSurface Energy ~> 72 dyne/cm(Hydrophilic)
-OH
-OH
-OH
-OH
-OH
Primer
Chlorinated Rubbers+CrosslinkerTop Coat
Rubber NBR / NR / EPDM Compound
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Dr. Hans-Joachim Graf 25
Example 1: Rubber to metal
Metal surface treatedSurface Energy ~> 72 dyne/cm(Hydrophilic)
-OH
-OH
-OH
-OH
-OH
Primer
Chlorinated Rubbers+CrosslinkerTop Coat
Rubber
What is the game?
Wetting + Chemical Reaction
Diffusion + Chemical Reaction
NBR / NR / EPDM Compound
Diffusion + Chemical Reaction
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Dr. Hans-Joachim Graf 26
Example 1: Rubber to metalSource: G.Polaski, et all, Lord Corp
Source: Bayer, Pergut broshure
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Dr. Hans-Joachim Graf 27
Example 2: Corner Moulding
➨ Profiles made of compounds based on EPDM
● EPDM Compounds bound with EPDM compounds
● TPV proven to bound on EPDM compounds
■ TPV: PP/EPDM base
Source: Toyoda Gosei
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Dr. Hans-Joachim Graf 28
Example: Corner Moulding
➨ Injection of Corner Moulding Compound based on EPDM
● Injection conditions■ Compound has ~ 100°C■ Mold Temperature ~ 170°C■ Thermal expansion result
pressure● Vulcanization time
EPDMProfile
CornerMoulding
Compound
Flow direct i on
DiffusionReaction eventually possible
Cold + crosslinked solid
Hot – low viscosity
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Dr. Hans-Joachim Graf 29
Example 2: Corner Moulding
➨ Injection of Corner Moulding Compound based on TPE-V
● Injection conditions■ Compound has ~ 200°C■ Mold Temperature ~ 50°C■ Thermal shrinkage result
pressure, compensated with after pressure
● Allow time to cool
➨ Some times called “Fusion Bonding”
EPDMProfile
CornerMoulding
Compound
Flow direct i on
DiffusionReaction eventually possible Cold + crosslinked solid
Hot – low viscosity
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Dr. Hans-Joachim Graf 30
Example 2: Corner Moulding
➨ What might hint the bonding?EPDMProfile
CornerMoulding
Compound
Flow direct i on
No Diffusion
Cold + crosslinked solid
Hot – low viscosity➨ Injection of Corner Moulding
Compound● And then no bond!● Condition: profile stored in
plant for a couple of days
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Dr. Hans-Joachim Graf 31
Example 2: Corner Moulding
➨ What might hint the bonding?● Water layer on surface● Water absorption change
polarity■ Drying with heat result
oxidation!?■ Plasma to remove water?
EPDMProfile
CornerMoulding
Compound
Flow direct i on No Diffusion
Cold + crosslinked solid
Hot – low viscosity➨ Injection of Corner Moulding
Compound (EPDM or TPV)● And then no bond!● Condition: profile stored in
plant for a couple of days
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Dr. Hans-Joachim Graf 32
Example 2: Corner Moulding
EPDMProfile
CornerMoulding
Compound
Flow direct i on
No Diffusion
Cold + crosslinked solid
Hot – low viscosity➨ Injection of Corner Moulding
Compound (EPDM or TPV)● Little change in surface energy
prevents diffusion● Effect is large, due to pressure
and time constraints●
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Dr. Hans-Joachim Graf 33
➨ System:● EPDM Adherent● PUR / VMQ Coating
● Wetting with Plasma■ Introducing of OH groups
in the surface■ Important: Must be the
„right“ amount.● Reaction with OH groups
■ Well known PUR chemistry
Example 3: Coating
In der Aufstellung fehlen die Coulomb-Kräfte
Source: Acheson/Henkel
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Dr. Hans-Joachim Graf 34
Example 4: TP - Rubber
➨ Injection Molding of a thermoplast “Vestoran” and Rubber
● Project TP-Rubber Part for the K ' 86 Fair in Düsseldorf (Jadamus, Richter)
➨ U.S. 4835063 and subsequent patents
● Vestoran – SBR rubber manufactured with moving platen technology
■ Investigation of Diffusion■ Worked, as long Rubber
was compounded with SBR / SBR Blend
Source: Graf, DESMA
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Dr. Hans-Joachim Graf 35
PPE-PS Thermodynamically compatible blend Interactions: 1 ) between aromatic rings 2 ) Styrene ether groups
PPE - SBR
Processing- compatibility
Creationboundary layer
Self adhesion Crosslinking layer
PPE - SBR/NR PPE - SBR/NBR PPE - SBR/EPDM
+ + + - + + +
+ + +
+ + +
- - -
H, W combine
1 2 3 4
PPE - EPDM no-one very low no-one Peroxide 5
HW
XXXX
H W
Cohesive rips through physical or chemicalphase connection
Source: Schuster, DIK
Example 4: TP-Rubber
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Dr. Hans-Joachim Graf 36
What help we get from this knowledge?
➨Rubber to metal● Cleaning● Contamination● Surface structure● Selection of Primer /
Cement● Layer Thickness
● Temperature-Time during loading
● Cavity Pressure● Forces during unloading
➨Rubber - RubberTP - Rubber
● Compatibility ● Production with no delay
time● Temperature - Time● Cavity pressure
● Environmental influences● Bleaching / Blooming of
Ingredients● Incompatibility● Contamination
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Dr. Hans-Joachim Graf 37
Summary / Conclusion
➨Rubber adheres with cohesive failure and high forces, if at least we have
● Contact + reaction● Contact + diffusion● Contact + diffusion + reaction
● It can have adhesion, it there is only contact, but the forces remain low