Written on: December 1, 2020 by W. Stephen Tait
Hello, everyone. The internal environment in spray packages (i.e. your formula) typically consists of multiple microenvironments and they, plus the package materials, determine if corrosion will occur and how fast it occurs.
Consequently, spray package corrosion comes in numerous forms, as illustrated in Figures 1–3 for traditional metal aerosol containers, spray valves and bag-on-valve (BOV) packages, respectively.
The approximate percentages on the right side of Figure 1 are the probabilities for corrosion occurring in traditional aerosol containers. Notice that the percentages add up to more than 100%—this means that multiple types of corrosion are possible for any given formula/package system.
The types of corrosion are classified under one of two umbrella classifications:
1. General corrosion, sometimes referred to as uniform corrosion
2. Localized corrosion such as metal pitting and coating/laminate film blisters
Corrosion can reduce package service lifetime in one of three ways:
1. Packages leak product or propellant
2. A package ceases to spray when metal corrosion occurs; loose pieces of coating or laminate film clog the valve
3. Metal ion contamination from corrosion diminishes product efficacy
Thus, package service lifetime is defined as the filled-package age when corrosion causes one or more of these failures.
Last month’s Corrosion Corner provided a graph that estimated the risk of corrosion versus time for different types of both spray packages and types of corrosion tests. The no-corrosion-data risk typically ranges from approximately 20%–60% depending on the type of package.
The old adage “A picture is worth a thousand words” rings true, so I’m going to provide photos of actual general and localized corrosion that caused reduced package service life (Note: A. Caridad, SPRAY Editorial Director, told me this writing style is referred to as “Zen Writing”).
The graph in last month’s Corrosion Corner also demonstrated that the corrosion risk from a one-year storage test is approximately 7% for aerosol containers and approximately 4% for BOV packages. The Aristartec electrochemical corrosion test technology has a less than 1% corrosion risk for both types of spray packaging after 90 days or fewer of testing. The risks for other types of electrochemical tests have either not been established, or are very high, such as the 84% risk for the driven can test.
Thanks for reading Corrosion Corner and I’ll be back next year. You can contact me at (608) 831-2076 or rustdr@pairodocspro.com; or from one of our two websites: www.pairodocspro.com and www.aristartec.com. SPRAY
