作者:Charles H. Trillich / Packworld USA联合创始人

热封技术已经发展了几十年，通过精确热封降低成本，增加利润。本文就这些进步以及如何每次都能获得完美的密封进行了反思。

近年来，由于过程控制的发展和引入，切割和/或密封塑料薄膜和连接塑料部件的方法和手段已经从一门艺术发展为一门科学，几乎可以保证每次都能完美结合。这种能力的发展是由关键应用中对塑料包装材料的需求驱动的，特别是在生命科学中，需要验证，失败是不可接受的。

热封塑料材料的艺术几乎是与热塑性材料本身的发展同时开始的。最初，材料的密封是通过简单的热棒或密封棒手工完成的。当手动密封时，密封的时间和质量是不一致的，取决于操作人员的技能。此外，当拆除密封装置时，密封件仍然是热的。由于塑料材料上的热密封只有在密封冷却后才会牢固地粘在一起，因此密封的完整性依赖于“热粘性”，即密封过程中膜层在仍然热的情况下相互粘在一起的能力。塑料薄膜被改良以增加它们的“热粘性”。这增加了薄膜的成本，但并不一定会提高最终密封强度。与此同时，非常重要的是要非常小心地处理温膜，以避免损坏密封的完整性或外观。在引入脉冲密封机之前，密封是由装有“热棒”或“热压板”的机器完成的。热棒和压板仍然用于冷却控制对特定应用不那么关键的应用。 Plastic sealing machines with “hot bars” use sealing bars that are constantly heated with cartridge heaters that are positioned within the bar as carefully as possible to deliver uniform heating to the sealing surface of the bars. Constantly heated bars and platens are useful in applications where the speed of the machine and the nature of the materials to be sealed offer a wide window of thermal opportunity. Some plastic film materials have a wide temperature range of seal-ability and will seal successfully in spite of a wide variation in sealing temperatures. However, many films do not offer a wide tolerance in the sealing temperature range. Most operations that seal or assemble plastic materials cannot afford the risk and attendant cost of creating defective products caused by a lack of time and temperature control. This is particularly true in packaging for healthcare, food, and precious or noxious materials. In the mid 1940’s “Impulse Heat Sealing” was introduced into the market. This was an important contribution to the art of heat sealing because it provided the opportunity to provide a momentary pulse of power through a relatively thin heating element that was pressed against two or more layers of plastic film. The energy supplied to the band produced enough heat to join the materials and the jaws could remain closed long enough for the seal band to cool and create an acceptable seal. The impulse sealing technique gradually gained acceptance and earned a significant share of the market, especially for sealing polyethylene and similar products. Early impulse heat-sealing machines could only be controlled by setting the voltage that is applied to the heatseal band and setting the timing of the sealing cycle. On manually operated machines, the duration of each cycle was determined from cycle to cycle by the skill of the operator because the temperature of the sealing band and bars became gradually warmer with every cycle. When an equal amount of energy is added to the sealing member with each additional cycle, the sealing temperature gradually rises and ultimately becomes too hot. Therefore, it must be frequently adjusted to avoid overheating

在20世纪70年代，德国TOSS GmbH公司认识到对高响应温度控制系统的需求。该系统必须持续监测热密封带的温度，以毫秒为单位将其温度提高到预定的设定值，并在预定的密封时间内将其保持在精确的设定值，以允许密封粘接和冷却。新系统还需要一种独特的合金来取代旧的镍铬合金热密封带。然后推出了TOSS Alloy-20，®。这种新合金能够预测和可测量地改变其电阻作为其温度的函数。超高响应控制器可以通过监测热封带电阻的变化来监测热封带的实际温度。

随着TOSS技术的应用逐渐展开，越来越多的定制包装机制造商适应了TOSS系统，以确保其机器的性能。提高精度的价值变得显而易见。这就产生了对专门使用TOSS技术的标准热封机生产线的需求。1995年，PackworldUSA应运而生。PackworldUSA进入市场生产热封机，其理念是精度，质量和耐用性是最高优先级。事实证明，这种理念是成功的。PackworldUSA机器的价值首先得到了医疗保健和生命科学公司的认可，在这些公司中，完美和工艺验证是必不可少的。其他行业很快意识到，耐用的精密热封机每次都能做出完美的密封，很快就能保住饭碗。

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