20. tri ethoxy vinyl silane
Primers - Silaneren – Chemical activation of a substrate
Y = vinyl of –CH=CH2
+ polyvinylbenzene (PS)
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3. Physical and chemical activation of the surface
eerst hydrolyse dan
binding op oppervlak
+ H2O
+ ROH
+ H2O
+ H2O
21. Physical activation of a surface by means of Plasma – flame – ai rplasma = corona
hoogspanning
electrode
Procesgas (lucht)
plasma
Surface-activation
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Distribution OH radicals in a turbulent
methane/air flame
=min
22. Activation of a surface by Surface cleaning
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Phosphatation (PO4)3-
Chromatation (CrO4)2-
Anodisation of a metalsurface (oxides)
Activation of a surface by the application of a conversion coating
23. Measuring Surface tension
Water:
* surface energy density of 0.073 J/m2 and
* surface tension of 0.073 N/m.
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H-OH 72,75 mN/m
CH3-OH 22,60 mN/m
CH3-CH2-OH 22,65 mN/m
HOCH2-CH2OH 47,20 mN/m
HOCH2CHOHCH2OH 63,00 mN/m
Glass 250 – 550 mJ/m2
Metals 200 – 1100 mJ/m2
26. 26/20
oil
Water , metals, glass, ceramics and wood are polar and Polyethylene & Polypropylene are oily!!!
-CH2- moistens everything!!!
Hydrophylic - hydrophobic
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POLYMERS
Water on an oily substrate
i.e. PE or PP
27. Compatibilty/Wettability
Liquids:
Surface Tension
1mN/m = 1 dyne/cm
De oppervlakte energie van het substraat moet hoger zijn dan de oppervlakte-energie van de lijm.
↑ 40 mN/m
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Solids:
Surface energy
1mJ/m2
mN/m
mJ/m2mJ/m2
mJ/m2 mJ/m2
28. 28/34
HO
OH
tack - “glueing” – sticking – hardening
Toughness elastomer
thermoplast
thermoset
OH HO O
Heat
Tack!!!
ADHESION
31. 31/34
The build up of POLYETHYLENE - PE
Molecular movement on a macromolecular scale
Entanglement
Pe is lighter than water
Pe is less dense than water
Polymers
33. https://www.techsil.co.uk/media/wysiwyg/pdf/Adhesive_Bonding_of_Polyolefin.pdf
https://www.google.com/patents/EP0476203A1?cl=en
“Thermosetting acrylic adhesives have been introduced that can bond
directly to many low surface energy plastics, including many grades of
polypropylene, polyethylene, and other polyolefin, without special surface
preparation.
This characteristic is believed to be due to diffusion of the acrylic
monomer into the substrate before cure.
It seems that the bonds formed on low density polyethylene result in substrate
failure and that an interphase of mixed adhesive and polyethylene is formed
up to 1.5 mm thick.”
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Joining of polyolefins by means of adhesives is not the most appropriate
way of joining. Polyolefins can best be joined through entanglement-
welding,
34. Cyanoacrylate adhesives do not wet or adhere well to polyolefins. The surface
tension of the adhesive is much higher than that of the substrate.
However, polyolefins can be primed for adhesion to cyanoacrylates by certain chemical compounds normally
considered to be activators for cyanoacrylate polymerization.
Materials such as long chain amines, quaternary ammonium salts and phosphine can be applied in either pure
form or in solution to the surface of the polyolefin.
It appears that one of the main reasons for improved adhesion by primers with
cyanoacrylate adhesives is that the solvents wet-out and swell the polyolefin. This
then facilitates interpenetration of the low viscosity cyanoacrylate resin.
These primers are simply sprayed or brushed onto the substrate. After drying of the primer, the cyanoacrylate
adhesive is conventionally applied and bonds extremely well to the substrate.
Triphenylphosphine or cobalt acetylacetonate primers used with cyanoacrylate adhesives produce adhesive
bonds with polypropylene and low density polyethylene that are sufficiently strong to exceed the bulk shear
strength of the substrate. They are also sufficiently durable as to withstand immersion in boiling water for long
periods of time.
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35. Primer [1]
Acrylate [3]
PE or PP
Acrylate adhesive
polymerized adhesive physically
bonded to (PE or PP) [4]
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swollen PE or PP [2]
36. Hechting op een substraat met een lage oppervlakte-energie [1] is eigenlijk een contradictio in
terminis. Hechting (moleculaire interactie) ontstaat als gevolg van de energietransfer van het
substraat naar de lijmmolecules.
Een hechting wordt dan ook bespoedigd door technieken toe te passen die de oppervlakte-energie
van een grondig gereinigd substraat verhogen (oppervlakte-activatie behandeling met plasma, vlam,
primers, sterke zuren etc…)
Anderzijds kan men er ook zorgen dat er zich vlot een intermolecuaire vernesteling voordoet tussen
met primer “ijler” gemaakte PE/EE-substraatmoleculen [2] en de geappliceerde polymeriserende
lijm-monomeermolecules (vloeibare acrylaten [3]). De groeiende lijmmolecules omkapselen hierbij
de olefinemolecules en verzekeren op die manier de hechting [4].
Maar eigenlijk is het evidenter om niet te verlijmen maar de tot smelten opgewarmde substraat-
staafjes, tegen elkaar te drukken. Tijdens het samendrukken van beide uiteinden zal er zich een
fysische cohesieve vernesteling voordoen van de molecules in de smeltzone. Dit leidt tot een intense
vernesteling of een aanzienlijke interactie/binding/adhesie over de contactzone (spiegel-, plasma-,
ultrasoon-, smelt- en hete lucht lassen). Bij deze alternatieve verbindingstechniek is de sterkte van
de verbindingszone gewoonlijk zelfs groter dan de treksterkte van het basismateriaal.
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