Page 192 - Handbook of Adhesion Promoters

9.8 Coatings and paints 185

9.8 COATINGS AND PAINTS

Coatings are the largest consumer of adhesion promoters. Commercial additives for vari-
ous coatings are discussed under numerous headlines in this chapter (aerospace, automo-
tive, coated fabrics, coil coating, flooring, metal coatings, etc.). The following commercial
additive trade names are used in coatings and paints: Amplify, Chartwell, Cylink, Eastman
Advantis and CP, Fusabond, Hypomer, Loxanol, Polypol, Qualicure, Sarbox, Silquest,
Sipomer, and Tyzor. The particular grades cannot be mentioned here by their names but a
full account of these additives can be found in a separate source entitled Databook of
Adhesion Promoters. The additives useful here contain acrylates, acrylic polyols, chlori-
nated polyolefins, ionomers, maleic anhydride modified polymers, monomers, phosphoric
acid esters, amino-, carboxy-, and hydroxy-silanes, and titanates as the main active com-
ponents. This means that many known adhesion promoters are useful to a degree in coat-
ings and paints.
The level of adhesion promoter (aminosilane) has a profound effect on the perfor-
1
mance of primer. Adhesion promoter tends to segregate onto the surface where it may
1
have an unexpected impact on adhesion between topcoat and primer.
Epoxy silane (glycidoxypropyltrimethoxysilane) was used as an adhesion promoter
2
in a duplex system (adhesion and corrosion protection). The films of silane formed on
galvanized steel diminished the corrosion current of the metal, but they did not protect the
2
substrate by a barrier effect. To improve wettability metal was degreased and barrier
o
2
effect was increased by drying silane layer for 1 h at 200 C.
Silicon alkoxides sol-gel pre-treatments (γ-glycidoxypropyltrimethoxysilane, tetra-
ethoxysilane, and methyltriethoxysilane) were used as adhesion promoters for metal sub-
strates (hot dip galvanized steel sheets, copper, and the AlSi Mg aluminum alloy) and
7
3
organic coatings (commercial powder coating based on polyester/epoxy blend). All sub-
3
strates were protected against delamination.
Chlorinated paraffins were used as adhesion promoters for paints on thermoplastic
4
olefins.
The effectiveness of γ-mercaptopropyltrimethoxysilane films as temporary corrosion
5
protection and adhesion promoter on electro-galvanized steel has been studied. The pro-
tection is affected by the coating curing conditions and the alcohol used for hydrolysis. 5
The silane curing on electro-galvanized steel sheets at 100°C improved the corrosion pro-
5
tection provided by the alkyd paint.
The steel panels coated with paint modified with polyaniline emeraldine salt have
6
the best protection after 720 h of exposure in 3.5% NaCl solution. Polyaniline works as
6
both corrosion inhibitor and adhesion promoter. The reversible redox properties might be
6
the reason for its ability to heal the metal surfaces before pitting corrosion sets in.
The adhesion behavior of polypropylene was improved by a combination of atmo-
spheric pressure plasma surface activation and silane adhesion promoter (tetraethoxysi-
7
lane).
The silane layer is a good adhesion promoter for the cataphoretic coating on galva-
8
nized steel and adhesion is maintained for long exposure times. A 120 nm thick silane
8
sol-gel film cured at 180°C ensures a very good compatibility with the electro-coat.