Once, processors either injection molded thin-walled packaging, or they thermoformed it, with the battle lines clear for all. But thermoforming’s advances have grabbed molders’ attention, so that molders’ expansion plans often now include adding thermoforming to their portfolio.
Many containers can be injection molded or thermoformed. Since the beginning of the plastics industry, the two methods have been largely practiced by completely separate companies. Injection molding machine builders have long been on the defense of their equipment with detailed studies, which always try to prove the better economics of their process. We extruder/thermoformers have never found such a defense necessary.
Rotary inline units could help thermoformers grab a share of the lid processing market.
With the rapidly increasing price of commodity polymers, things have changed recently: Many of the major injection molders have entered into thermoforming by the acquisition of one or more companies in that business in order to remain a competitive supplier of containers, particularly to the dairy market.
The reason is simple: orientation strength, which is only obtainable by thermoforming because it is done below the melting point of the polymer, particularly with polypropylene. This produces cup-shaped containers such as those used for dairy products with much thinner walls but having the same compression strength as their injection molded equivalents.
Furthermore, injection machines used to have much larger capacities than thermoforming machines were capable of, and these also required a two-stage process: sheet extrusion followed by forming. Now most large-volume thermoformers are run directly inline with their sheet extruders, and capacities in the 6000-lb/hr range or even higher are available. These far exceed anything available in the equivalent molding range, and tilt the economics of large-volume thin-walled containers even more in that direction.
Nevertheless, the sheet extrusion/thermoforming process requires more skilled attention than injection molding, which can be turned on and off rapidly with little attention besides the correct settings of temperatures and cycle times. Sheet extrusion lines take several hours to preheat, and they require additional time to settle down once started up, plus some careful die and takeoff adjustments with which former injection molders must learn to live. While the transition has sometimes been painful, the results ultimately have been successful and have resulted in a large market conversion in that direction.
Another large difference between the two methods is the market pricing of their machine time or return on investment. I see regular publication in the trade press of the current cost at which injection machine time is available on the market. Figures of far less than $100/hr come to mind for machines costing close to $1 million. No sheet extruder or thermoformer would ever sell at such low and simplistic prices. They think more in terms of $1000/hr return on a sheet line that costs well over $1 million plus the cost of the thermoforming machine operation. This is partially justified by the greater skill required by that process, but has resulted in some severe belt tightening in the industry, as well as some costly learning on the part of the novices.