Decorative properties of Type II, functional properties of Type III.
Sanford Process says its new Micralox micro-crystalline aluminum anodic coating packs molecules in a regular, ordered and repeating pattern that makes it suited for reusable medical instruments, equipment and devices that require repeated cleaning and sterilization because of its enhanced chemical stability.
According to Jack Tetrault, company president, the coating is thermodynamically stable with a lower solubility rate when exposed to harsh chemicals such as the acids and alkalines frequently found in common detergents.
“Many commercial parts commonly require sulfuric acid anodizing, either in a softer, decorative Type II or hard but dark Type III,” Tetrault says. “Type II is primarily used to generate a thin, clear film on parts that can be dyed a variety of bright colors and be finished from dull matte to high gloss. Due to the low current densities used to form the coating, the finish is susceptible to scratching and abrasion.”
However, Tetrault says it is possible to have the decorative properties of Type II with the functional properties of Type III using Sanford’s low-voltage hard-coat process.
He says on the company website that, previously, the aluminum finishes of choice were all conventional aluminum anodic coatings—amorphous solids where the microstructure of the anodized coating consists of molecules in a random arrangement, with no short-range order.
“Consequently, these anodic coatings are less stable and more prone to dissolution, and rapidly break down in the presence of strong chemistry (either acids or bases),” Tetrault writes. “This leads to loss of protection of the substrate, discoloration and premature corrosion of the coated component. While keeping the same chemical composition, Micralox partially converts the amorphous oxide into partially micro-crystalline structures, resulting in significantly enhanced chemical stability.”
Each reusable medical device has a designated cleaning protocol prescribed by the manufacturer. This requires removal of biological and other contamination, and the choice of processes and the detergents varies depending on where the device will be used. In Europe, stronger detergents with higher pH are common as they are perceived to be more effective in combating prior diseases.
However, conventional anodic-coated aluminum parts and ancillary equipment may display dulling, fading, mottled surfaces and evidence of corrosion following cleaning cycles, Sanford Innovations Director Mike Sung says.
“This type of corrosion is typically not related to salt water, but rather the dissolution of the coating,” he says. “The key variables determining this occurrence and rate of failure are chemical agent and pH concentration of cleaning detergents, temperature of wash/dry cycle, residual chemistry on surface after rinsing, and overall exposure time.”
Sung says that amorphous oxide coatings are partially phase-changed to micro-crystalline structures developed in a low-voltage, hard-coating process that fundamentally changes chemical resistance.
“The molecular arrangement of the amorphous-form molecules are random and less stable and dissolve more readily,” he says. “Partially converting to a crystalline form rearranges the molecules into a regularly ordered, more tightly packed repeating pattern that is more chemically stable and has lower solubility. Thus, micro-crystalline structures dissolve at a significantly lower rate.”
Tetrault says that Micralox coatings can be colored in a wide range of colors, and the process protects the coatings from fading due to heat oxidation. It also protects dyes from oxidation during the Sterrad sterilization process.
In addition, since all medical devices are required to be fully traceable by the manufacturer, Sanford also has introduced Sanford Print, a process for embedded printing in the oxide entrapped below the seal. Sanford Print helps protect the embedded print from fading due to autoclave and Sterrad sterilization.
“While epoxy ink printing is normally used, thermal cycles during cleaning and sterilization may cause adhesion loss due to different rates of expansion and contraction, and handling leads to chipping,” Tetrault says. “Biofilms formation in print abscesses is difficult to eliminate, and sterilization methods may lead to print fading, as occurs with colored parts in general. n
Information for this article provided by Sanford Process. For more information on Sanford Process, please call 877-899-2734 or visit Sanfordprocess.com.