Jaws, heat-seal

The packet thus formed was filled with the food product to be tested and the open side was heat sealed. Heat seals were usually made at 350°F jaw temperature, 40 psi pressure with 0.5 second dwell time the exact conditions necessary depend on the materials used and caliper. This produced a packet with an 8 sq. in. total area. 

It is used as a coating for heat sealing jaws, as a low friction surface and as inert coating for rubber stoppers. 

PTFE is a very hard, chemically inert, low-friction material. It is mainly used to coat machine parts (to reduce friction) and heat sealing jaws to aid clean release. It is not used as a lamination film but has been used as a coating on closures (densities up to 2.2). 

Filling end. Heat seal, heat weld with cooling jaws usually essential (avoid presence of product). Also ultrasonic welding, hot air sealing, plus cooling jaws, etc. 

Decoration should not lift, flake or crack under conditions of heat and/or pressure, e.g. heat sealing or the application of pressure sensitive tapes, i.e. substrate surface lifts. Heat seal jaws may be coated with PTFE to reduce ink pick . 

The serrations can be cut at various included angles, and have various numbers of teeth per inch, and are usually truncated as shown in Fig. 6.11. This approach minimizes the cutting of the structure during heat sealing. There are many different serrated seal jaw designs available from equipment manufacturers and film suppliers. A thorough discussion is beyond the scope of this book. 

Throughput, speed, possibly as metres per minute, how sealed by platen or rotary principles, how cooled and cut. Release following seal compression (jaw release)—depends on seal design, cleanliness of jaws, surface characteristics of materials, possible buildup from lacquers, varnishes, surface pick, pressure of inks, etc. External temperature applied and conductivity through to seal layer, cooling and cooling interfaces (air-metal, metal-metal and heat sinks), etc. 

Hot bar weldii employs simple heating jaws or bars, one or both of which are continuously heated to a temperature of between 180°C and 230°C. The temperature is thermostatically controlled. To prevent the plastics being sealed from sticking to the heated bars, a barrier material such as PTFE is interposed between the plastics film and the heated bars. The bars are normally attached to a small pedal press or hand tongs, but in the case of high output requirements, the heated bars are an integral part of a purpose made equipment. An example is a polyethylene bag making machine, which operates at well over one seal/second per webb run. 

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