The Different Types of Medical Pouch Sealers
Medical pouches are sealed in different ways, depending on the type of pouch material being used, the sealing temperatures needed, and other factors. The four most common types of medical grade heat sealers are: constant heat, impulse heat, rotary band, and form fill seal (F/F/S).
Constant heat sealers
A constant heat sealer is typically a “jaw type” sealer, with seal dies that repeatedly open and close, sealing one pouch at a time. A constant heat sealer has a heater embedded into its aluminum sealing die. The operator turns the machine on and selects the appropriate recipe. After a short period of time (approx. 10 minutes), the die is heated to the set temperature and the heat is evenly distributed across the sealing die, and the die will remain at this temperature until the sealer is turned off or a different temperature is selected. Because the die is heated to one temperature and it remains at that temperature until either the set point is changed or the machine is powered OFF, constant heat sealers are the easiest heat sealers to validate. They also provide the most stable, repeatable sealing process and require less ongoing maintenance than other types of sealers.
For these reasons, constant heat technology is the preference of most medical device manufacturers. Typically, constant heat technology is used to seal the three sides of the pouch when it is made —and so, it is the technology that will provide the best, most compatible seal across the final, or fourth, side of the pouch.
Impulse heat sealers
Like constant heat sealers, impulse heat sealers are usually also “jaw type” sealers; however, the heating element of an impulse heat sealer is a very thin wire that can heat up and cool down quickly. As a result, after an “impulse” of heat is generated, the die rapidly reaches temperature and then cools down, all while under pressure. The operator can keep the die closed as the heating element cools and the pouch material drops below the melt point to a temperature that allows the pouch to be removed from the sealer and handled without worries about it being tacky or damaging the seal.
Impulse heat sealers are typically used for either the high temperature sealing or welding of mono-layer materials. They are not preferred when sealing pouches made from multi-layer materials because when the temperature fluctuates between heating and cooling every cycle, it is difficult to maintain accurate process control.
The most common method for monitoring the fluctuating seal temperature on impulse heat sealer is with a thermocouple, which measures the temperature and sends that signal back to the temperature controller. Impulse sealers require very fine thermocouples because the finer the thermocouple, the faster the response. (which means they are likely to need frequent replacement). Note: Every time maintenance is required on a medical grade heat sealer to replace a critical component that is part of either the temperature delivery, pressure delivery, or the time delivery system, the sealer needs to be re-qualified.
Rotary band or continuous band heat sealers
A rotary band or continuous band heat sealer is not a “jaw type” sealer that seals one pouch at a time. Instead, a continuous band or rotary band heat sealer uses opposing bands to carry pouches through the heat sealing process. The operator feeds the leading edge of the pouch into the sealer, where it is captured by the bands and pulled through to the section where heat is applied. The heat brings the materials to the melt point and welds them together, and then the bands continues to pull the pouch through the sealer to an unheated section where cooling occurs. The cooled pouch then emerges from the other end of the machine.
The advantage of a continuous band or a rotary band heat sealer is throughput. It offers significantly higher output compared with a jaw type heat sealer. In addition, a continuous band sealer is optimal when the two sides of the pouch are the same material (similar materials have the same thermal expansion rate and dissimilar materials can expand at different rates which can result in wrinkles in the seal). Rotary band sealers are also optimal for products that are light weight, flat, and lower profile. Rotary band sealers can operate in a horizontal or vertical orientation.
Interestingly, a continuous band or a rotary band heat sealer offers the benefits of both constant and impulse heat. The actual pouch sealing is done with constant heat, which is a very stable temperature, but then the pouch is pulled along to an area where there is no heat, enabling it to cool under pressure.
Form fill seal heat sealers (F/F/S)
A form/fill/seal machine does not use preformed pouches. Instead, it uses two rolls of material that come together in the middle of the machine to actually create the pouch around the product. The operator places the product, either manually by using automation, into the sealer and then the sealer uses a set of reciprocating dies to create a sealed pouch around it. Form/fill/seal machines can be horizontal of vertical.
Form fill seal machines are used for high throughput, high output requirements. In fact, they can usually run as high as 20 plus cycles a minute. However, tool change overs for form fill seal heat machines can be time-consuming because in these instances, seal dies and cutting mechanisms need to be replaced. By contrast, with a traditional impulse sealer, constant heat sealer, or rotary band sealer that uses a preformed pouch, there are no full-on changeovers, enabling operators to move easily and quickly from one type of pouch to another.
For any of these heat sealers to be used for medical pouch sealing, they should be ISO 11607-compliant. ISO 11607 is a guidance document that is used to define many different aspects of sterile packaging. For example, for a piece of sealing equipment to be ISO 11607-compliant, it must have the ability to verify and alarm temperature, pressure, and time.