Page 181 - Handbook of Adhesion Promoters

174 Selection of Adhesion Promoters for Different

8.29 TPO

Many commercial adhesion promoters can be used in TPOs, including Amplify, Eastman
Advantis, AP & CP. There are too many products to be listed by their names here but a full
account of these additives can be found in Databook of Adhesion Promoters which also
contains additional information on the use
of these additives.
Thermoplastic olefins utilized for
interior and exterior automotive parts are
painted to protect and enhance their appear-
ance. They possess a low surface energy
and adhesion promoters such as chlorinated
polyolefins, are used to increase paint
adhesion and improve paint performance. 1
Chlorinated polyolefin properties depend
on the chlorine content and molecular
1
weight. The diffusion depth of chlorinated
polyolefin into the TPO is less than 1 μm
and it consists only several mass percents. 1
The chlorinated paraffin forms a separate
layer between paint and TPO (see Figure
2.28). The modulus of the higher chlorine
content or higher molecular weight chlori-
nated polyolefin did not change with the
1
processing method.
The topcoat adhesion to thermoplastic
olefin was determined in the presence of
2
gasoline. The adhesion was promoted by
the use of solventborne chlorinated poly-
2
olefins. The topcoats were either one-com-
Figure 8.10. Interface morphology and z-directional ponent melamine crosslinked systems or
profiles of TPO25/CPO/TPO25, a lap shear joint sub- two-component isocyanate crosslinked sys-
jected to baking at 120°C for 20 min. (a) Stiffness map; 2
(b) z-directional intensity profile from the white line in tems. Adhesion of the coatings in the pres-
(a). [Adapted, by permission, from Deng, K; Winnik, ence of gasoline was directly proportional
MA; Yan, N; Jiang, Z; Yaneff, PV; Ryntz, RA, to the depth of diffusion of chlorinated
Polymer, 50, 14, 3225-33, 2009.]
polyolefin into the substrate and the resis-
2
tance of the clearcoat to gasoline permeation.
The rearrangement of polypropylene crystallites at the uppermost surface under a
3
120°C bake accounted for the increased cohesive strength of the painted composite.
A maleated chlorinated polypropylene containing 21.8 wt% Cl was used as adhesion
4
promoter for injection molded plaques of TPO. A “transition zone” was observed
4
between adhesion promoter and the TPO. The zone exhibited enhanced stiffness after
annealing at 120°C. Annealing (120°C/20 min) led to broadening of the interface between
4
TPO and adhesion promoter (Figure 8.10). A higher stiffness in the transition zone cou-
4
pled with a thicker interface resulted in a stronger adhesion and cohesive failure. The
interfacial structure between the adhesion promoter and the TPO was probed by TEM