Adhesive-primer coat failure

CM - Cement/Metal failure failure at the primer to metal interface. For one coat adhesives, this is failure at the adhesive to metal interface. 

An intrinsic disadvantage of DPO methods is that failure occurs at the weakest part of the coating system. This can occur cohesively within a coating layer adhesively between coating layers, especially if the glue has created a weak boundary layer within the coating or adhesively between the primer layer and the metal... 

Chemical treatments are usually most effective with aluminum alloys, especially when long-term environmental exposure is required. The sulfuric acid—dichromate etch FPL etch, named after Forest Products Laboratory, US Department of Agriculture www.fpl.fs.fed.us) has been used successfully for many decades. Techniques more recently developed are often modifications of the FPL procedure. Other important methods include chromate conversion coating and anodizing. Corrosion-resistant adhesive primer, as well as anodic and chromate conversion coatings, helps to prevent corrosive failure of adhesion. ... 

Figure 4 shows the insulative ability of the above formulation. Three coats were applied over a primer to a total dry film thickness of 20 mils, allowing 24 hours dry time between coats. This graph indicates complete failure in 8 minutes. When subjected to other tests the coating lacked adhesion to metal, moisture resistance, and flexibility. After, puffing, the coating disintegrated under vibration. 

Keywords Cracking Adhesion GMOD Polycarbonate Siloxane Topcoat Primer Automotive Glazing Coating Degradation Hardcoat Entitlement Fracture Mechanics Cycling Temperature Humidity Time-to-failure... 

Fig. 7.6 Comparison of GMOD failure modes for coatings on black substrates. In contrast to the clear sample GMOD failure data of Fig. 7.5, here cracking (solid symbols) is a much earlier failure mode than adhesion (open symbols). Additionally, the two failure modes show opposite trends with primer thickness. In this graph, the lines are drawn to guide the eye rmd do not represent fit equations to the data (Note Test results. Actual results may vary)...

O Fig. 8show. The total oxide thickness is 400 nm. This type of nanoroughness can provide more mechanical interlocking than most other treatments for improved bond strength and durability, but this increase occurs in the interlocking only if the polymeric polymer or adhesive completely wets and penetrates the pores of the oxide. The nanoscale pores create capillary forces that help this penetration. Cross-sectional SEM views of PAA coated with typical epoxy primers show such penetration (Venables 1984). In such cases, strictly interfacial bond failure is very unlikely. 

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