What type of products are being sealed in the trays? Food, medical devices, other? What capacity are you looking for: 50 a day, 5,000 a day? Will the end product be hand placed in the tray, or will the trays be loaded via some automation process? Will the package be sealed under pressure, vacuum or neither?
These are the types of questions you need to be asking yourself before you can begin to look at the design of the packaging system.
Most trays are thermal-sealed, where a heated platten presses a thin film around the sealing edge of the tray. The trays themselves can have a wide array of materials, and the film has to be compatible with this material for proper sealing. The plattens are usually made of an aluminum alloy, that matches the tray seal area, and are coated with teflon-like materials that can withstand the sealing temperatures. "The attempt and not the deed confounds us."
All I am in need of knowing, is how the film is cut after sealing. I assume that there is a top blade that would be profiled to suit the requisite shape of tray. Does this blade cut thro the film into a rubber gasket, or is the cutter system more like a die with a male piece above and a female below.
I've seen both approaches. Usually it's just a steel rule die cutter with male and female components. using rubber to cut against introduces a maintenance issue that most poeple would rather not have to deal with. "The attempt and not the deed confounds us."
Can't help you there... but try searching on Google for "food tray sealing" or "food packaging" and you'll get a ton of sites with pictures (though not detailed) of sealing equipment. You might be able to gleen something from them. "The attempt and not the deed confounds us."