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ANODIZING to allow it to "cure." Cold seals produce a chemically resilient finish, and in the case of many dyes, will improve fade resistance. Duplex seals are often used in the automotive industry due to the enhanced corrosion protection they provide. The standard duplex seal is a sequential process where an initial dip in a hot nickel acetate solution is followed by a boiling water treatment. A variant of this is the little-known Hi-Barrier Dual seal, which exchanges the boiling water treatment for a dip in a hot silicate solution. Silicate seals are known to improve the coating's alkali resistance. Unpublished research has shown that substitution of a standard cold seal for the hot nickel acetate step will further enhance alkali resistance beyond that which the silicate dip alone provides. This sequence is referred to as a Modified High Barrier Dual seal. Studies have suggested the suitability of a similar process for producing automotive trim parts to meet the rigorous pH 13.5 test used in that industry. Experimental AA6061 sheet stock was used throughout our experiments. Panels were alkaline soak cleaned, etched, deoxidized, and anodized for 45 min. at 15 amps per sq. ft. to create a porous coating measuring 0.7 – 0.8 mil thick. The panels were then colored using the conditions listed in Charts 1-3. Each pre-cut colored panel was carefully split into strips, and each strip was sealed using conditions listed in Chart 4. In the case of the inorganic colors, only seals 1-7 were used. Two sections taken from each of the 95 color/seal combinations were submitted to Advanced Sterilization Products to be processed in a Sterrad 100NX Sterilizer for 100 standard cycles. Every 10 cycles, the samples were removed and washed. A comparative visual assessment of each of the colored finishes before and after undergoing 100 Sterrad sterilization cycles is shown in Chart 5. Panels that survived the treatment without notable fading are identified by a dark green box; panels that completely faded are indicated in red. Discussion An oxidative environment—such as a Sterrad sterilization cycle—can fade anodized coatings that are colored with organic dyes. Multiple cycles can do so catastrophically. It has, however, been demonstrated that dyed coatings can be produced to withstand 100 such cycles with no noticeable effect. With the correct seal system, Sanodal Red B3LW, Yellow 3GL and Green 3LW are among a list of dyes that can be successfully used for this application. On the other hand, Sanodal Deep Black HBL, Blue G and Turquoise PLW should not be used regardless of the seal system. It is not known why some dyes can and others cannot be used and therefore impossible at this time to predict the applicability of other dyes. With the exception of the unsealed reference series (No.7), the seal treatments used in this study were all of very high quality. Even so, for the most part they failed to protect Chart 4 ID Type Additive Time Temp. pH 1 Boiling water 3 g/L Anodal SH-1 45 min. >205°F 5.7 2 Boiling nickel 7 g/L Anodal ASL 45 min. >205°F 5.5 3 Hot nickel 20 mL/L Anodal MS-1 New 20 min. 180°F 5.8 4 Step 1: Cold seal Step 2: Hot water 3 g/L Anodal CS-3 3 g/L Anodal SH-1 15 min. 15 min. 85°F 160°F 6.0 5.7 5 Step 1: Cold seal Step 2: Hot nickel 3 g/L Anodal CS-3 7 g/L Anodal ASL 15 min. 30 min. 85°F 160°F 6.0 5.5 6 Step 1: Hot nickel Step 2: Boiling water 7 g/L Anodal ASL 3 g/L Anodal SH-1 10 min. 45 min. 160°F >205°F 5.5 5.7 7 No seal - reference n/a n/a n/a n/a 8 Step 1: Hot nickel Step 2: Boiling silicate 7 g/L Anodal ASL 20 mL/L Anodal Si1000 15 min. 15 min. 160°F > 205°F 5.5 11 9 Step 1: Cold seal Step 2: Boiling silicate 3 g/L Anodal CS-3 20 mL/L Anodal Si1000 15 min. 15 min. 85°F > 205°F 6.0 11 Step 1: Cold seal Step 2: Hot nickel Step 3: Boiling silicate 3 g/L Anodal CS-3 7 g/L Anodal ASL 20 mL/L Anodal Si1000 15 min. 15 min. 15 min. 85°F 180°F > 205°F 6.0 5.5 11 10 26 DECEMBER 2013 — pfonline.com