Primers based on spherical zinc dust and Micaceous iron oxide
Primers based on spherical zinc dust and Micaceous iron oxide(MIO) The preparation of zinc rich primers was based on a semisolid epoxy resin, a polyaminoamide adduct-like hardener, spherical zinc dust and the MIO. Paints were formulated with a pigment volume concentration (PVC) from 40 to 65%; the volume ratio of zinc dust and MIO was 1:1. The partial replacement of spherical zinc dust by MIO was examined with PVC = 65%; the ratio between spherical zinc dust and MIO was changed to 83:17, 67:33 and 50:50, respectively. The pearl mill was used for preparing the primers.
The basic properties of paint films were evaluated. The anticorrosive effect of single-layer paints and the paint systems were also determined. Such characteristics as drying time, pendulum hardness, cupping test, impact resistance, bending test and adhesion were tested over four weeks.
New degreased and ground steel panels were used for the tests. The size of the panels was 100 by 150 by 1 mm. Single-layer coatings of zinc-rich epoxy primers with a dry thickness of 60 ± 5 µm were prepared. Protective paint systems consisted of one coat of zinc-rich epoxy primer and two-component acrylic polyurethane as the finish coat (dry-film thickness of 160 ± 15 µm). In all cases, the panels were prepared in triplicate and stored for four weeks for hardening at /23 ±2/ °C and /50 ±5/ % relative humidity.
The single-layer coatings and the paint systems were exposed to:
- Salt-spray (fog) testing according to ISO 9227
- Humid atmospheres containing SO2-cyclic accelerated corrosion tests: eight hours in a humidity cabinet with SO2 and 16 hours in the ambient atmosphere-ISO 3231.
Anticorrosive protection of the paint systems was evaluated according to ASTM D 1654-92, D 610-85 and D 714-87. Heubach rating was used for testing of anticorrosive effects-100 is the best and 0 is the worst.
The adhesion of the paint systems was evaluated as cross cut test ISO 2409. The adhesion was tested before the beginning of corrosion tests and after completion of these tests.