Gas impermeable plastics suitable for ultrasonic welding
Gas impermeable plastics suitable for ultrasonic welding
(OP)
I am looking for suggestions of a plastic I can use as a gas impermeable package. The key is that this plastic needs to have a low permeablility, good strength, and also be suitable for ultrasonic welding. Any help or advice would be greatly appreciated





RE: Gas impermeable plastics suitable for ultrasonic welding
Butyl rubber is not a plastic, but has very low gas permeability.
Matweb.com has gas permeability coefficients listed for a variety of polymers, typically films. Some films are less permeable to polar molecules, and vice versa, and thus you may find that a multi-layer composition would work best, depending on the mix of gases you are trying to seal.
RE: Gas impermeable plastics suitable for ultrasonic welding
RE: Gas impermeable plastics suitable for ultrasonic welding
RE: Gas impermeable plastics suitable for ultrasonic welding
RE: Gas impermeable plastics suitable for ultrasonic welding
We once had an interesting discussion, during a design review, about whether we needed a bladder, a pressure relief valve, or some such, to handle the pressure changes from temperature in the pressurized dry nitrogen we were putting into a test instrument. When the system was actually built, the first time we purged the system, it was so leaky that the pressure drop to ambient in about 30 seconds.
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RE: Gas impermeable plastics suitable for ultrasonic welding
RE: Gas impermeable plastics suitable for ultrasonic welding
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RE: Gas impermeable plastics suitable for ultrasonic welding
Chris DeArmitt PhD
President - Phantom Plastics LLC
Consulting, ideas and training on plastic materials
www.phantomplastics.com
RE: Gas impermeable plastics suitable for ultrasonic welding
RE: Gas impermeable plastics suitable for ultrasonic welding
I think you can ultrasonically weld the films and have them hold up okay, but as CP said, I think these are multi-layered films where an inner bondable layer for welding is included in the construction. The films are produced with the idea that impermeable bags be made from them, for e.g. food products and/or medical products where oxygen spoilage or contamination with water vapor are issues.
"Is it possible to mold mylar?"
Getting low permeability from a molded part is more of a crapshoot, for reasons the real experts above have noted. It is possible to add metallization, and other barrier coatings, which can affect permeability.
"the permeability of the pastic will need to be low enough so the nitrogen will not leak for the life of the part. "
That is a non starter, in my opinion, but you don't state what the "life of the part is" - I'm assuming something more than 1 year. It might be possible with a fairly heavy metallized polymer, multi-layer construction. That said, I'm not certain that even the metal can with epoxy seal would hold up for multiple years - has that ever been tested? I.e. if this is an arm-wave goal and not a hard spec., and the real requirement is that the unit simply function well over the years, then maybe.
What is the real reason for the nitrogen blanket - is it to prevent moisture intrusion? Oxygen intrusion? There are absorbers or "getters" for these contaminants, which if included inside the capsule could help.
RE: Gas impermeable plastics suitable for ultrasonic welding