Nonchromated primer coating

Figure 28.9 Comparison of chromated primer coated A1 panel ([7B](Dox)/T/F/A) with nonchromated primer coated A1 panel ([7B]y(Dox)/Tfs/(Ar)/X) after Prohesion salt spray test primers were removed after the test.

Table 31.3 summarizes the adhesion test results of nonchromated primers [Spraylat EWAE118 (D) and Dexter 10-PW-22-2(X)] to plasma coatings deposited without an anode assembly, which were produced in both flow and closed system deposition processes. As noted in Table 31.3, closed system TMS plasma polymers (Tcs) showed superior primer adhesion performance to similar ones obtained from a flow system (Tfs). Similar to chromated primers, summarized in... 

Figure 31.30 Scanned images of Prohesion salt spray-tested A1 panels coated with nonchromated primers prepared in a flow or closed reactor system without using anode assembly Primer X could not be removed from plasma-treated [2P] and [7P] surface due to the strong adhesion.

In order to produce chromate-free plasma coating systems, the adhesion of closed system TMS coatings to nonchromated primers (Spraylat EWAE118 and Dexter lO-PW-22-2) was also investigated, and the adhesion test results are summarized in Table 32.9. Closed system TMS plasma polymers showed superior primer adhesion performance to those obtained from a flow system. Similar to chromated primers, summarized in Table 32.8, excellent primer adhesion was always achieved with closed system TMS plasma polymers treated with subsequent Ar plasma applications. 

A nonchromated, water-borne primer applied to [2B] alloy samples, with the appropriate surface preparation and plasma deposition of an ultrathin plasma polymer, was also compared to controls prepared by depositing a chromated primer on chromate conversion-coated A1 substrate. The same comparison was also performed for IVD Al-coated 2024-T6 substrates (pure aluminum is deposited by ion vapor deposition process on aluminum alloy 2024-T6). In the latter case, the primer could not be removed from the IVD Al-coated panels that were treated with the plasma polymer prior to spray primer application. It is interpreted that the water-borne spray paint penetrates into the column structure of the top surface of the IVD Al-coated substrates when the surface energy was modified by the application of a plasma polymer. This effect could be viewed as interactive coating with a porous surface. 

A PPG cathodic E-coat, designated E2, was used. The chromated spray primers employed were water-borne Deft 44-GN-36 (A) or 44-GN-72 (Al) (Deft Corporation, Irvine, CA) and solvent-borne Courtauld 519X303 (G) (Courtauld Aerospace, Glendale, CA). The nonchromated spray primers were water-borne Dexter lO-PW-22-2 (X) (Dexter Corporation, Waukegan, IE) and water-borne Spraylat EWAE118 (D) (Spraylat Corporation, Chicago, IE). 

The main aim of SAIE is the complete elimination of heavy metals from the coating systems an approach that primarily relies on tenacious water-insensitive adhesion and good barrier characteristics of a primer has been taken. It should be pointed out that this approach is theoretically incompatible with the approach that utilizes the primers with corrosion inhibitors, e.g., chromated primers. This is because a primer with super barrier characteristics would not allow the migration of inhibitors and would not provide enough water for their electrochemical reaction to form corrosion protection products, as described in Chapter 28. In order to further elucidate the SAIE concept, both chromated and nonchromated spray primers were employed to generate two types of plasma coating-modified systems, and their corrosion protection behaviors were investigated in this study. 

The complete elimination of heavy metals and other hazardous compounds from the coating systems was the main objective of SAIE. Chromated spray primers with hazardous chromate components do not fit such an objective. Therefore, two kinds of nonchromated and water-borne spray primers, Spraylat EWAE118 (D) and Dexter lO-PW-22-2 (X), were selected to produce chromate-free plasma coating systems for corrosion protection of A1 alloys. 

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