United States Department of Transportation
i
Measurement of adhesion properties between topcoat paint and metallized/galvanized steel with surface energy measurement equipment.
-
2013-09-01
-
[PDF-135.63 MB]
Details:
-
Creators:
-
Corporate Creators:
-
Corporate Contributors:
-
Subject/TRT Terms:
-
Publication/ Report Number:
-
Resource Type:
-
Geographical Coverage:
-
Corporate Publisher:
-
Abstract:The objectives of this research project are: (1) Compare the adhesion properties of NEPCOAT-approved topcoat paint over
metallized or galvanized steel. Use “surface-energy” measuring technique to characterize the wetting properties of the liquid paint
on the profiled zinc surfaces. Explore correlation between the adhesive strength and the liquid paint wetting properties. As control
the adhesion properties of topcoat paint over zinc primer painted steel substrates will also be measured. (2) Investigate various
factors affecting the adhesion of topcoat paint over galvanizing. (3) Report and recommend practices that produce the best adhesion
of NEPCOAT-approved topcoat paints over metallized and particularly galvanized steel surfaces. We prepared four different types
of test panels coated with five different commercial paint systems. The paint systems include four systems adapted from the
NEPCOAT list of intermediate and top paints qualified for bare steel, and one system of epoxy sealer for metallized surface. Four
types of substrates were used for fabricating the test panels: (1) galvanized steel with mechanical grinding to produce rough
surface, (2) galvanized steel with blast profiling to produce rough surface, (3) galvanized steel stored indoors for two weeks before
blast profiling and painting, and (4) metallized steel with inherent roughness due to the thermal spray process. We recorded, as a
function of time, the contact angle of droplets of freshly prepared liquid paints on the replicas of the substrate used for spray
painting. The cured test panels were subject to pull-off strength tests according to the ASTM D4541 standard, and the X-cut tape
tests according to Method A of ASTM D3359 standard. Images of the pull-off test break surfaces were photographed and
examined. We analyzed the correlation between the pull-off strengths and the contact angles. The correlation provided insight on
the relative adhesive strengths of the different paint-substrate pairs. We concluded that (1) the NEPCOAT paints could be used for
galvanized and metallized steel to obtain comparable adhesion performance as that of the zinc-rich organic primer coated steel, (2)
although the NEPCOAT intermediate paint on the metallized surface has adequate pull-off strength to pass the inspection, it is
highly recommended that the state DOT specification of the use of sealant is strictly followed, (3) although the exposure to
atmosphere after galvanizing is commonly recognized as a problem for paint adhesion, we found that a time delay of two weeks
between galvanizing and profiling/painting is permissible if the galvanized steel is stored in the normal indoor dry atmosphere, (4)
we think a refined quantitative correlation between pull-off strength and contact angle could be useful for optimizing the paint-tosubstrate
match.
-
Format:
-
Collection(s):
-
Main Document Checksum:
-
Download URL:
-
File Type:
