Chromated primer, coating system

Figure 31.28 Scanned images of Prohesion salt spray-tested A1 panels with chromated plasma coating systems prepared by anode magnetron plasmas Primer G could not be removed from the whole Al panel due to the strong adhesion, and only the portion with pitting corrosion occurred underneath could be stripped off with paint stripper solution.

Since it was observed that fluorine contamination was a possibility and had potentially detrimental effects as described in Chapter 10, the excellent primer adhesion achieved with Tfs/(Ar) and Tcs/(Ar), shown in Table 31.3, has significant importance in the practical application of the plasma technique without any of the potentially deleterious effects of fluorine-based systems. Argon plasma treatments on both flow system TMS (Tfs) and closed system TMS (Tcs) polymers were then investigated as an additional system modification that could provide strong adhesion without the incorporation of fluorine-containing monomers in the quest to produce chromate-free coatings systems. 

Figure 32.4 Average corrosion widths of SO2 salt spray-tested IVD aluminum-coated 2024-T3 and 7075-T6 A1 panels, including chromated controls, IVD/plasma polymer/E-coat, and IVD/plasma polymer/spray primer coating systems.

This system, also submitted by exhibitor B, consisted of one coat of fire-retard-and zmc chromate primer, followed by application of a fire-retardant semigloss white. 

The vinyl copolymers can be used most efficiently in special applications such as hospital and dental equipment where durability is more important than initial cost. For laboratory equipment, epoxy resins may be preferred because the vinyls are sensitive to some solvents. The vinyl coating systems consisting of corrosion-inhibiting primer and chemical-resistant finish coats are used on new equipment for chemical plants. The metal conditioner based on zinc chromate and polyvinylbutyral are widely used over sandblasted steel as a use for vinyl systems on both industrial and marine equipment. 

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. 

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 31.29 summarizes the corrosion widths along the scribed lines that were calculated from (1) SO2 salt spray-tested and (2) Prohesion salt spray-tested A1 alloy panels and their corresponding control panels. As seen from Fig. 31.29, the corrosion test results showed that the plasma coating systems based on the chromate-free spray primers provided excellent corrosion protection for the A1 alloys studied. 

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. 

It should be emphasized that the primers in the plasma coating systems applied to the IVD Al-coated A1 alloys could not be removed by the commercial Turco paint stripper solution. This tenacious and water-insensitive adhesion at the primer/IVD interface achieved by TMS cathodic polymerization in a closed reactor system must be responsible for the excellent corrosion protection performance of these plasma coating systems. In other words, excellent corrosion protection of IVD Al-coated A1 alloys can be accomplished with chromate-free primer coatings with the aid of tenacious and water-insensitive interface adhesion. 

Substances Control Act (TSC A). In May 2006, the Occupational Safety and Health Administration (OSHA) implemented new, stricter regulations regarding workplace exposttre to chromates especially hexavalerrt chrome. Polymeric coating systems containing tare earth compound inhibitors that provided corrosion inhibition in a similar manner have been developed. Replacement of the chromate compotmds used in the primer coating with tare earth-based material removes >95 wt% of the hexavalent chromium contained in the coating system. 

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