HEAT SEALERS
Senior Editor
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Custom designed heaters ensure even heat distribution across the sealing area in Sencorp heat sealers, such as in the 12-DDS/2 Deep Draw Vacuum Chamber Constant Heat Bar Sealer.
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Although heat sealers often feature advanced technology for controlling and monitoring seal production, the process of manufacturing sterile barrier systems requires validation. Packagers must establish with a high degree of confidence that processes repeatedly make seals that conform with package design specifications.
The 2006 revision of ISO 11607, and accompanying AAMI guidance document Technical Information Report (TIR) 22, provide medical device firms with clearer, more precise guidance for validating processes.
The new TIR 22, for example, details procedures for completing installation qualification (IQ), operational qualification (OQ), and process qualification (PQ). It also sets out recommendations for process control and process monitoring. In accomplishing these steps, the guidance stipulates that packagers must establish a testing protocol, followed by documentation of test results.
“TIR 22 walks you through the entire validation process with step-by-step actions for engineers to follow,” says Dhuanne Dodrill, president, Rollprint Packaging Inc., and chairperson, ASTM committee F02.50, Package Design and Development. “The information has been available, but the new guidance organizes it into one place, dealing specifically with ISO 11607 requirements.”
“In the areas of process control and process monitoring, we are trying to provide guidance on some of the tools and approaches that can be used.” For example, TIR 22 Annex E discusses material processing requirements, Annex F addresses process induced defects, and Annex H details tools that can be used to identify what is critical in the process, Dodrill says.
While the new ISO standard and TIR 22 guidance give engineers a better road map for completing process validation, there is still some confusion over requirements for worst-case testing that are referenced in ISO 11607 Parts I and II.
“It’s clear that people are struggling with how to interpret and address each of the clauses addressing worst-case requirements,” says Dodrill.
Worst-case testing of the sterile barrier system manufacturing process is addressed in two sections: ISO 11607-2, Clause 5.1.5, and ISO 11607-1, Clause 6.3.4. (ISO 11607-1, Clause 6.1.6., a third area where worst case is addressed, pertains to identifying the worst-case configuration of the medical device product that puts the most stress on the packaging system.)
Clause 5.1.5 says that packages that have different configurations (such as different-size seal areas) but use the same top and bottom materials, may be grouped into families. The worst case or the extreme configuration or configurations in the family (e.g., the largest pouch or the smallest pouch) are identified. The worst case is validated to establish that the sealing window will work for all packages in the family. “You don’t want to have to validate 10 different packaging sizes of the same material,” says Dodrill.
Clause 6.3.4 says that worst-case packages should be tested at the specified process limits of forming and sealing—those limits established in the OQ. For accomplishing this, two approaches are described. The choice of approaches will vary among manufacturers, but in each case should be supported by an appropriate rationale that is included in the documented validation protocol, Dodrill says.
In the first approach, sampling is employed on preformed pouches run at normal operating conditions within the validated window. “If the sample size is large enough, you are assured of seeing the full range of package characteristics (including packages made at the edges of the sealing window),” says Dodrill.
Using this approach, packagers might avoid the time and expense of running multiple lots for producing worst case pouches sealed at extremes of temperature, pressure and dwell. Manufacturing the fourth side of the pouch at worst-case parameters, however, is recommended for providing additional safety assurance, Dodrill says.
“The general consensus is that when using premade pouches, the pouches can be sourced with sterile packaging manufacturers’ seals made at normal operating conditions,” she says. “However, the final closure seal should be made at the worst-case conditions of manufacture within the validated window. [When sampling is employed], this provides additional assurance that you are testing packages made at the worst-case extremes.”
In the second approach described in clause 6.3.4, all seals are made at the extremes of the validated window, whether sourced as premade pouches or form-fill-seal-manufactured.
“These are different approaches for accomplishing the same result,” says Dodrill. “The end result of worst-case testing will be that the manufacturer is comfortable that the range of seal strengths produced within the validated sealing window meet package specifications.”
MACHINE ALARMS
To assist customers with validation, most heat sealer vendors provide an initial machine calibration. Vendors will recommend parameter settings to help customers define the minimum and maximum settings established in the OQ process. Sencorp Inc. (Hyannis, MA) provides complementary sample IQ/OQ protocol documents with machine purchase, says Lynne Barton, marketing manager.
“Sencorp offers standard specification information, and sample pouch sealing if requested,” Barton says. “We recently provided a customer with photographs of sample pouches before and after sealing, and a videotape of our technician performing the sealing process.” The sealed samples were mailed back to the client, so it could complete in-house peel tests.
Heat sealers offer various controls for ensuring production of specified packaging, as well as options for auditing and verifying machine performance. Many heat sealers will alarm out or shut down if bags are being manufactured outside the validated seal window. In sealers that are adequately calibrated, validated, and regularly maintained, this feature provides high assurance that bags are being produced according to specification, vendors say.
“Customers will have unique sets of criteria for sealing parameters, based on the materials they are using,” says Brian Jobson, product manager, PAC Machinery Group (San Rafael, CA). “We establish that the sealer can perform according to their sealing requirements, and verify that the machine will alarm out if those parameters are exceeded.”
Emplex Bag Sealing Solutions (Toronto), a division of PlexPack, manufactures continuous sealing machines that are loaded without waiting for a seal cycle. “Audio and visual alarms, and reverse feeds, have been the basis of validation on continuous sealing machines since the mid 1990s,” says John Lewitt, vice president sales. “If the bag exits the machine, you know your validated parameters have been met.”
Although alarm settings provide some assurance that seals are being produced within the validated sealing window, medical device packagers have sought machines with the capacity to monitor sealer functions, for confirming and documenting seal cycle repeatability and consistency.
Temperature control is most commonly employed with a controller corresponding with a thermocouple fixed to the heating bar or band. Impulse medical sealers from PAC Machinery and Aline Heat Seal Corp (Cerritos, CA), for example, feature systems with proprietary controllers that maintain band temperatures within 1 or 2 degrees of the set point. Temperature reading instruments can be connected to external ports for verifying the accuracy of the temperature control system.
These firms mapped their bands to demonstrate consistent heat dispersion. PAC Machinery performed tests on its medical impulse sealers in which independently controlled thermocouples were set every four inches on the element. The tests showed variations within one or two degrees across the seal length, says Jobson.
BAND MAPPING
Aline mapped its MPD table top pouch sealers, with nine measurements at the left, right, and center. Heat values were within one-and-a-half-degrees across the band, and within one-and-a-half-degrees of the set point, says Charles Schapira, president.
As impulse sealers repeatedly cycle in pouch production, temperature tends to build up in the band and the aluminum bar mount. The residual heat causes the temperature set point to be reached faster in later cycles.
To manage this temperature variability, seal timing starts only after the band reaches the set point. On PAC Machinery’s impulse sealers, this method ensures that bags are always sealed at the same temperature, for the same dwell time, says Jobson.
“The sealing is not affected by the ambient temperature of the band and the bar, since we don’t start the timing until we reach the set temperature,” Jobson says.
To ensure bag seals are cooled to the same temperature point, the impulse units allow setting a low temperature set point, after which the seal cycle ends, Jobson says.
“We can use water cooling of the bar to manage heat build up, and allow a faster cooling cycle,” he adds.
Schapira notes that the PLC in Aline impulse sealers can be programmed to increase rise times to temperature, for customers requiring more production speed. When faster rise times are used, the temperature setting might over-shoot by up to ten degrees, as power sent to the band is accelerated, he says.
“The PLC will correct for the over-shoot in milliseconds, returning the band to the set point. A small over-shoot is not that significant, because most materials tolerate a fairly wide sealing window,” he says.
Sencorp ensures an even heat profile across the constant heat dies in its medical pouch and tray sealers using custom designed heaters within the dies that control and distribute the heat predictably. The heaters are single zone, “which assures that the temperature distribution cannot change over time as a result of a dead zone or a dead heater in a multi-heater design,” says Barton. “Temperature is controlled at a single point, with additional thermocouples at multiple points on the die for monitoring purposes.”
PROCESS CHECKING
Barton says that dwell time in Sencorp sealers is controlled either through discrete timers or PLCs. The units feature output ports for external calibrated timers. “The timer is activated by an optical switch when the dies make contact. If anything causes the timed cycle to terminate before the set [dwell] time is achieved, the system will alarm and the machine cannot be cycled again until the alarm is acknowledged,” she says.
Data acquisition systems are an option for medical device firms seeking to document their sealing values. Emplex is offering a flash drive on its continuous sealers as a low-cost alternative to a PC for capturing sealing output. Heat, pressure, and speed values on the continuous band units are monitored every three seconds and written to a flash card on the machine, from which they can be uploaded as wanted to a PC.
“This solution provides a convenient method of data capture without the need for an expensive PC on the production floor. This system is ideal for customers that have had product recalls and need to increase documentation of their sealing procedure,” Lewitt says.
Process control can also involve controls on equipment manufacturing. Belco Packaging Systems Inc. (Monrovia, CA) demonstrates and documents that one heat sealer performs identically to another, supporting the interchange of tooling between its shuttle-style sealers.
“More and more customers have multiple machines,” Tom Misik, vice president of sales, says. “If you have to shut down a cleanroom, the heat sealer is taken out of the production flow. We provide verified specifications for machines of the same size and model, so the user can transfer the affected healing fixture to any other Belco same style machine and perform a process qualification only.”
The use of impulse versus constant heat sealers depends on the package materials used.
“With constant heat you lose the benefit of the cooling cycle where some of the bonding occurs,” Schapira says. “When sealing poly/poly bags with constant heat, bubbling tends to occur. Seal defects will be minimized if you are using a laminated foil, because the foil tends to cool down on its own.”
“For sealing Tyvek pouches, most customers are looking for a minimum pound-and-a-half per square inch seal,” he adds. “Constant heat can be used in applications where speed is an issue. However, you need impulse for additional bonding time if you are sealing for a higher pounds per square inch.”
Barton notes that various steps can be used to address material sticking issues.“These include different types and textures of Teflon cloth (on the sealing surface), different coatings applied directly to the dies that offer different release characteristics, and mechanical solutions that hold the pouch in place as the die pulls away.”
In the heat sealing industry, end-users have driven the advances in machine technology, vendors say. Packagers are willing to pay more for enhanced features that support process consistency and machine validation. PAC Machinery recently customized its Med Vac sealer for a major international packager that sought additional safety functions, says Ian O’Rourke, marketing manager.
The Med Vac Plus medical pouch sealer features work-surface height adjustment, and a Lexan jaw cover for shielding the seal area from operators’ hands. Hand safety switches can be used to prevent high pressure engagement of the jaws until they are less than 1 mm from the sealing surface.
“We do not take a boilerplate approach to machine development, or how we support customers with validation, as we have discovered that each production environment is unique. In short, we support each client on a case-by-case basis, and work closely with them to provide the highest level of equipment compliance possible, because you compete in this industry on customer service,” he says.
