The word you may encounter is "expensive." Just from interacting with consumer items that have such seals, they are typically placed where there is a readily accessible surface.

I can imagine a plunger device with a vacuum that holds the foil in place, moves into the cylinder to the stop, and then uses a heater or ultrasonic welder to melt the plastic layer on the aluminum.

If the foil is held with cold adhesive, then it probably requires special processing to place the adhesive on the rim of either the cylinder or the edge of the foil.

I do agree. I was actually thikning the same but wasn't sure how expensive that would get.

what job does a "foil cap liner" do ? resist pressure ? keep dirt out of the tube ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

it does seperate the ingredients. Cap liner acts as a gate between two ingredients

so it sees some load ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

That's correct..

how much ? what pressures ?? ... you aren't making this easy.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

I would say 1N force from Top

Have you studied the way those seals are normally applied? Are you planning a comparable production rate?

Presumably an end user is going to need to open this at some point. Do you have a plan for that?

Can this be done by making the part in two pieces with the heat seal applied to the top of the lower piece first (conventional) and then attaching the upper piece to it by some other suitable means?

Is it critical that there is an absolute seal, or is some leakage acceptable ?

What durability ??

How does this tube work with the rest of the device ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.