In all instant films there are components that are heat sealed. "Heat Sealing" is joining or sticking parts together so they form an assembly. A good example of a heat seal is the chemical pod that spreads the developer in all instant films. The quality of this heat-sealed seal affects how the chemicals spread, or not.
Other parts are heat sealed too. For instance, the air tight bad that the film is wrapped in is heat sealed. This is a simple operation compared to the pods, which is more complex.
The distribution of heat, how long it is applied, and pressure on the seal greatly affects how well the seal performs. In our case, we produce a frangible seal. This is a special type of seal designed to break open at just the right pressure, and requires very precise pressure and temperature.
Various industries are trying to make tools to measure sealing performance and sealing tool quality. Here is such a tool: It produces a color-coded map of pressure, which could be useful. One thing that is shown here is an acoustic horn, which is part of the business end of an ultrasonic welder. Instead of just being hot, ultrasound waves are transmitted into the material to heat it up by just the right amount.