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What type of metal and finish for a food storage container

January 20, 2009

I am designing a kids food tray that has divided compartments for the food. Imagine a deep cafeteria tray with a rubberized exterior bottom surface. I'd like to avoid using plastics, but don't really know the properties of various metal and finish options. The material must be lightweight, dent resistant, scratch resistant, food safe (preferably FDA compliant or approved), non-corrosive (with contact to a variety of foods including acids), inexpensive (this is a kids product afterall!) and not transfer flavors to food. If it can be bonded to silicone that would be a bonus since the rubberized bottom will likely be silicone. What type of metal and coating would be best?

I have been considering stainless steel, aluminum, and enamel coated mystery metal (like they use for camping dishware) without the benefit of any technical expertise.

Any guidance on what metal, with what coatings or finishes, and what manufacturing processes would fit the bill would be appreciated.

Thanks for your help!

Eva Selig
Product designer - Mill Valley, California, USA

First of two simultaneous responses -- January 21, 2009

18/8 or 304 stainless is the best fit for your described needs. It is roughly the same price as hard coated aluminum and is extremely durable. Dents are a minor inconvenience. Passivization would be appropriate and if you want it to be initially shiny, it can be electropolished. It can be formed and bonded. Is there a good reason for the silicon/rubber coating of the bottom?

James Watts
- Navarre, Florida

Second of two simultaneous responses -- January 21, 2009

Dear Eva,
I will leave the choice of metal to the experts... my input would be, the coating needs to be antibacterial. There are antimicrobial powder coating materials now available based on added Silver... either in nano or ion format. Silver has been used for 1000's of years to prevent
wounds from bacterial attack. It is non-toxic, tasteless etc additive. You could specify Silver ions as an additive to the silicone and plastic/paper/cloth.
Terry Hickling

Terry Hickling
Birmingham, United Kingdom

January 23, 2009

The rubberized bottom is to keep it from sliding around on the table. But much of my research indicates that the process by which silicon is bonded to metals is quite labor intensive and therefore expensive. (The metal part is primed before placing it onto a mold where liquid silicone is injected. It is the curing time of the primer that is most expensive.)

I'm also finding that the cost differential between stainless and anodized aluminum is quite significant. The aluminum is less than half. James, is the "hard coated aluminum" that you refer to the same as anodized? Or something different. And would anodized be suitable for my application?

And Terry, thanks for the input on the silver. I hadn't heard that one before.

Eva Selig
- Mill Valley, California

January 27, 2009

Hard anodize is significantly more dense and thus more chip resistant than conventional sulfuric (type 2) anodizing. It is what you find on cookware, with or without teflon.
The aluminum is softer than SS, so will dent easily or require a thicker metal.

James Watts
- Navarre, Florida

February 3, 2009

Hard anodized aluminum is a good choice except that with prolonged exposure to highly acidic foods it is eventually attacked. Also in some cases strongly alkaline and poorly formulated dish washing compounds will eventually attack the anodize making it white and chalky. On the plus side anodize can be impregnated with silver. But still, as much as I'd like to promote anodizing, I'd go with stainless steel.

Leo Herringon
- Grand Rapids, MI, USA

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