Detachable coating compositions

Detachable coats based on latexes are much cheaper. Their compositions are based on water dispersions or emulsions of the following polymers ... 

Another polypyrrole/polyamide composite film was obtained by the electrode coating method [84]. In this work the polyamide film was obtained in situ by coating a stainless steel electrode with a polyamic acid film followed by imidization with pyridine and acetic anhydride. The coated electrode was submitted to a constant current in a pyrrole/LiC104 solution in acetonitrile. The surface conductivity measured after detaching the composite film from the electrode showed a strong dependence on the charge density used in the synthesis, i.e. on the amount of pyrrole polymerized in the composite. The maximum value obtained was 2 S cm . Combination of polypyrrole with this polyamide was shown to increase markedly its thermal and environmental stability. 

Apart from the chemical composition of the substrate, the surface finish is also important. It has been found that surface defects such as scratches and inclusions act as nuclei for accelerated film growth. The resulting film defects extend above the normal film surface, for example in the form of nodules, which may be far larger than the original substrate defect. These defects represent weak points, and may be detached in service leaving holes in the film coating. It is therefore important to ensure that the substrate surface is smooth and uniform in texture and composition. 

Detachable or removable paint coats are applied from compositions on the base of polymers in organic solvents or aqueous latexes. 

Incorporation of nanosized SiC particles in the EL NiP matrix increased the hardness from 627 43 to 704 60HVqqj. However, incorporation of micronsized SiC particles increased the hardness to 1669HVqqj. The cumulative mass loss versus time (see Fig. 8.26) due to cavitation erosion corrosion in 3.5% NaCl is found to be very low for EL Ni-P-nano SiC composite coating compared with its coimterpart incorporating micron-sized SiC particles. The EL Ni-P-nano SiC coated specimen exhibits a smooth and uniform surface after the cavitation erosion corrosion test with no visible pits (see Fig. 8.27). The uniform distribution of the nanosized SiC particles in the EL NiP matrix (R 0.95 0.060 pm) inhibits the formation of pits. However, the higher surface roughness (R 1.72 0.051 pm) promotes bubble formation and causes detachment of the SiC particles, which results in the formation of small cavities on the surface of EL Ni-P-micro SiC coated steel (see Fig. 8.27). Hence, it is evident that incorporation of nanosized particles in EL NiP matrix could provide a better cavitation erosion corrosion resistance and inhibit the onset of erosion damage near surface defects. 

The principle of the EN ISO 4624 2003 pull-off test requires a dolly to be glued or soldered to the composite panel. An increasing pull-off force is then applied to the dolly until the coating detaches from the substrate. The adhesive strength of the bond is calculated from the maximum force applied and the size of the detached area. If failure occurs elsewhere than between substrate and metallization, it is essential to add a reference to the fracture pattern as a supplement to the measured value. 

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