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© Fraunhofer IFAM 1st product with pre-applied adhesive (PAA) Not acceptable by the market without PAA Invention in 1840 revolutionised any kind of mail and logistics
© Fraunhofer IFAM
1st product with pre-applied
adhesive (PAA)
Not acceptable by the
market without PAA
Invention in 1840 revolutionised
any kind of mail and logistics
© Fraunhofer IFAM
Vorapplizierbare Strukturklebstoffe - ein neues
klebtechnisches Konzept für die industrielle
Fertigung
Pre-applicable structural adhesives - a new
bonding concept for industrial production
Andreas Hartwig, Andreas Lühring, Matthias Popp, Manfred Peschka
Fraunhofer-IFAM, Bremen
Suppliers Convention & Hannover Messe, Hannover 2014
© Fraunhofer IFAM
Pre-applied adhesives (PAA) are widely used for
non-structural applications
E.g. stamps, PAA with ...
... activation by moisture ...
... or PSA and removal of release paper
© Fraunhofer IFAM
Pre-applied adhesives (PAA) are widely used for
non-structural applications
Or envelopes
Moisture activation
PSA, removal of release paper
Contact adhesives
© Fraunhofer IFAM
Pre-applied adhesives (PAA) are widely used for
non-structural applications
Sticker and labels,
removal of release paper
Foto: © Klicker/ www.pixelio.de
© Fraunhofer IFAM
Application of PAA in structural bonding?
Pre-Applied Structural Adhesives = PASA®
Use of the Fraunhofer IFAM PASA® technology will improve product
design, productivity and quality!
PASA® are usually solid and tack free at ambient conditions
© Fraunhofer IFAM
Motivation
Application of PASA® has numerous advantage compared to liquid or paste
adhesives:
Handling of parts with adhesive becomes simpler as both are already
connected.
No harm of contamination by the adhesive during assembling.
Adhesive application can be carried out at different places than assembling.
Sealing of a prepared surface by the PASA®.
No use of liquid chemicals during assembling required.
© Fraunhofer IFAM
Requirements on PASA®
Quick
curing but
long shelf live
Tack free but
good wetting
Good
adhesion on part
in uncured state
PASA®
© Fraunhofer IFAM
Chemistry of PASA®
Most commercial adhesives are not sufficient for (real) quick curing.
Bubble formation and britteling occur.
Controll of shelf live difficult, increase of viscosity not obvious.
Application and processing outside typical conditions, but in other branches
adoptable solutions available.
Right chemistry combined with processing teaches how
to prepare parts with tack free, highly reactive
adhesives.
© Fraunhofer IFAM
I. Dual-cure with different curing reactions
Property profile:
Liquid or paste like adhesive.
After UV-irradiation formation of a tackfree, thermoplastic adhesive layer.
Thermal activation, adhesive melts and wets second part followed by chemical
curing.
Chemistry:
Acrylate or methacrylate combined with epoxy resin.
Curing step 1: Radical polymerisation of the acrylate or methacrylate by UV light.
Curing step 2: Thermal cross-linking of the epoxy groups, e.g. by dicyandiamide.
© Fraunhofer IFAM
II. Thermally curable dispersion of solid resin
Property profile:
Dispersion of a solid adhesive in water.
After evaporation of the water a homogeneous, tackfree, thermoplastic and reactive
adhesive layer is formed.
Thermal activation: melting and cross-linking.
Chemistry:
Dispersion of solid epoxy resins combined with latent hardener (e.g. dicy,
microencapsulation, urones or imidazoles.
© Fraunhofer IFAM
III. Thermally curable hot melt
Property profile:
Tackfree up to 50°C
Melting 70-100°C
Curing > 100°C
Adhesive preparation:
Mixing of the single components in the melt below curing temperature. Very proper
control of preparation conditions!
Application:
Application as melt, alternatively powder application with sinter process.
Chemistry:
Reactive, solid epoxy resins on the base of bisphenole-A, novolak and the like.
© Fraunhofer IFAM
Example 1: Bonded fastener
© Fraunhofer IFAM
Bonded studs as fastener for transportation industry
Application of small amounts of liquid adhesives in
automotive assembling not acceptable.
Pre-applied thermally reactive hot melt based on
epoxy resin,
Quick curing in some seconds.
Tackfree up to 50°C.
Combined development of heating process,
adhesive formulation and design / stud geometry.
Development of a process for adhesive
manufacturing and application required.
© Fraunhofer IFAM
Adhesive production and application
Flexibilisator
+
Härter
+
(Füllstoffe)
Harz
+
Füllstoffe
M M
Zuführung
Dosierung
Mischung
Applikation
Flexibilisator
+
Härter
+
(Füllstoffe)
Harz
+
Füllstoffe
M M
Zuführung
Dosierung
Mischung
Applikation
Mixing of components in molten state:
low temperature and short time,
otherwise reaction starts
Studs with PASA®
(real studs applied in automotive look
much different)
© Fraunhofer IFAM
0 10 20 30 40 50 60
0
50
100
150
200
Te
mp
era
tur
[°C
]Zeit [s]
Temperature during inductive heating
Curing process: Inductive heating
Very high heating rates.
Proper controll of heating process.
Automatisation possible.
© Fraunhofer IFAM
0
5
10
15
20
25
0 5 10 15 20 25 30 35
Erwärmungszeit [s]
Zu
gsch
erf
esti
gkeit
[M
Pa]
Lap-shear strength of an epoxide based hot melt PASA® on AlMg3 without pre-treatment
Adhesives properties
Quick curing and bond formation.
Tackfree at 50°C.
High strength on different substrates.
Tolerant against contaminations.
© Fraunhofer IFAM
Example 2: Bonded blanks
© Fraunhofer IFAM
Local reinforcement of sheet metal
Production of parts with lower metal thickness lightweight constructions.
Local reinforcement difficult, use of past like adhesives does not fit in the
production conditions of sheet metal parts.
New way of adhesive bonding required for production of such parts.
Reinforcement of engine hood at
the lock as example.
© Fraunhofer IFAM
Process
VB PASA®
GB
Coil
base
coil
reinforce
coil with
PASA®
Cutting Fixation, spot welding Deep drawing KTL
Adhesive application on the coil or metal sheets.
PASA® forms tackfree layer and coil can be wound up.
Final curing in KTL or other oven.
© Fraunhofer IFAM
Adhesives development
After test of different concepts use of an epoxy resin dispersion as base adhesive.
Requirements, beside the typical things:
Cutable wihout contamination of tools.
Deformable together with sheet metal during deep drawing.
Tackfree at room temperature.
Good adhesion in uncured state.
Long shelf life.
etc.
© Fraunhofer IFAM
Formulation of the adhesives
Amount [%]
Resins
Pudis12 29,50%
Epis316 49,16%
Fillers and Additives
Inikor3c 9,83%
Addis14 0,39%
Water 9,83%
Hardener
Hady12 1,28%
Amount [%]
Resins
Pudis12 33,33%
Epis316 33,33%
Fillers and Additives
Water 32,50%
Hardener
Hady12 0,90%
Start formulation:
Formulation after first improvement:
Strength: 16,5 MPa (oily steel)
18,3 MPa (degreased)
(Curing: 180°C, 30 min.)
- Corrosion of the
steel observed
Strength: 14,6 MPa (oily steel)
20,6 MPa (degreased)
(Curing: 180°C, 30 min.)
- No corrosion
© Fraunhofer IFAM
Bending test with the not cured adhesive
• Adhesive with PU: no
change during bending
test
• Adhesive without PU: no
adhesion, breaks during
bending
PU as additive improves adhesion and most other properties
© Fraunhofer IFAM
Test of deep drawing properties by Erichsen deepening
• Not cured adhesive with
PU.
• Adhesive layer fails at
high deformation degrees.
• Cured adhesive with PU.
• Very good adhesion and
failure of the steel.
© Fraunhofer IFAM
For fixation of the two sheet metals spot welding is
required
Process of spot welding
Quelle: TU Chemnitz
Sheet metal
Adhesive
Welding electrode
Sheet metal 2
Welding electrode
Electrical connection required.
Adhesive layer between sheet metal
pieces to be bonded which leads to
electrical insulation.
Adhesive must be removed / pressed away
which is no problem for liquid adhesives.
Spot welding works well with the new adhesive!
© Fraunhofer IFAM
Examination of the welding spots yields proper
connection through the adhesive
DP 800
5mm
600μm
5mm
H 340
© Fraunhofer IFAM
Demonstration: patch work in automotive part
Thickness decreases
/ harm of breaks or
failure
Sheet metal thickness increases during
deep drawing
Local reinforcement of the sheet metal
possible.
Reduction of total thickness of the sheet
metal leading to lighter construction
and lower cost.
© Fraunhofer IFAM
bottom die
geometry of engine hood die and blank holder
geometry of engine hood
pocket to hold
the inlay die part of the blank
holder
Work performed by IFUM (Hannover University)
Demonstrator: patch work in automotive part
© Fraunhofer IFAM
Demonstrator: proper local reinforcement
© Fraunhofer IFAM
Demonstrator
PASA® was applied on coil.
Reinforcement of engine hood was successful.
No problems during KTL.
Springback of reinforcing sheet metal sometimes critical.
Adhesive layer partially too thin work on
application of thicker layers.
© Fraunhofer IFAM
Expire of adhesives shelf-live?
In case of non-structural adhesives
fixation with other methods possible.
Tape
Mechanical fastener, the staples are
obviously not the perfect solution.
© Fraunhofer IFAM
Control of shelf-life
Adhesive and substrate form a uniform part.
Expire of adhesive shelf-life means that the complete part can not be used any
longer.
Application of additional adhesives or mechanical fastener not possible like in
non-structural bonding.
Parts logistics and control of the adhesives state must even be more perfect
than in conventional production.
© Fraunhofer IFAM
Control of shelf-life and cure state simple by colour reaction
PASA® changes colour if the shelf-life is
expired and by having a different colour
completeness of cure can be checked
visually.
Can also be transferred to other
adhesives.
fresh expired
cured
© Fraunhofer IFAM
Conclusions
Proper combination of chemistry and processing enables the development of
adhesive sufficient as PASA®.
really quick curing with good bond properties.
long and controlled shelf-life.
tackfree at ambient conditions.
Visual inspection of shelf-life and cure state is possible and can be transferred
to other adhesives.
PASA® has the potential to improve assembling in industrial production
significantly and might become the second revolution in which pre-applied
adhesives are involved after invention of the stamp.
© Fraunhofer IFAM
Thank you for your most valuable …
… your time and attention.
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