20 Years of Heat Sealing
Published: June 7th, 2013
Heat sealers have improved by increments and leaps, driven by industry guidance, FDA scrutiny, and the requirements of medical device companies for machines that consistently engender compliant seals.
In the past two decades, heat sealer vendors have devised more user-friendly machines that are easier to validate and maintain. With the advent of PLCs and electronic control of sealing processes, packagers could with greater precision set, monitor, and control the sealing parameters of temperature, pressure, dwell time, and speed.
Machines came with monitoring ports for supporting machine calibration and validation for showing evidence that sealing performs consistently to package design specifications with a high-degree of assurance.
“The technology has advanced 10 to 15 years in the last five years,” observed Kent Hevenor in 1999, then product manager—laboratory machinery, Sencorp Systems Inc.
“Suppliers have made huge strides in meeting industry demands. Now the question is, is there a more cost-effective and efficient way of doing the same thing? We have to revisit less-expensive ways to accomplish the same thing without compromising quality,” Hevenor said.
“Customers are driving better machines, whether to provide data collection or to cut costs. The machines have to be more versatile because they have to run a lot more materials and products than before,” said Ann Marie Kellett, marketing manager, O/K International Corp that year.
Issued in 1997, ANSI/AAMI/ISO 11607 “Packaging For Terminally Sterilized Medical Devices” provided industry with guidance on process validation requirements. Yet the guidance was seen as too open to interpretation. A wide range of methods for qualification and validation were being used in meeting FDA Quality System Regulation.
With the release in 2006 of a revised ISO 11607, with accompanying AAMI Technical Information Report 22, industry had more precise and clearer guidance on validation, with recommendations for process control and process monitoring.
Heat Sealing Milestones
1993 – Delta Industrial rolls out a rotary heat seal module and a new line of modular in-line web packaging systems for 12” and 18” web widths.
1995—Packworld USA introduces a line of medical impulse heat sellers equipped with variable resistance temperature controls known as TOSS Technology.
1997—publication of ANSI/AAMI/ISO 11607 “Packaging for Terminally Sterilized Medical Devices”.
2002—In medical pouch constant heat sealers and tray sealer dies, Sencorp offers one-piece single-zone blanket style heaters for predictable control and distribution of heat across the sealing area.
2003--Van der Stahl Scientific offers new machine sealer with polarized pressure feedback system.
2003—Packworld USA with TOSS Technologies introduces the all-electric PW7016 to meet the industry requirements for validation.
2003—Aline Medical Packaging introduces Precise-Seal impulse sealer with PLC and PID control for maintaining a heating element range of plus or minus 1 degree F.
2004--Atlas Vac Machine, division of Planet Products Corp., provides the Direct Force Sensing System using load cell technology for measurement of sealing force; and the Infrared Vision Temperature Sensor for immediate reading of actual sealing platen surface temperature.
2004 – Delta Industrial debuts the Delta Mod-Tech Reciprocating Heat Seal Module, a new addition to the Delta Mod-Tech module “tool box” that offers customers a more accurate seal and permits a variety of patterns.
2004—Packworld USA with TOSS technology develops high temperature sealing machines for sealing various forms of PTFE used in cryogenic applications.
2005—ANSI/AAMI/ISO 11607 “Packaging For Terminally Sterilized Medical Devices” is revised in a more comprehensive and easier to follow form, in two parts: materials and package design, and validation requirements for manufacturing processes. The revision harmonizes ISO 11607 with EN 868, and incorporates CEN standards. Technical Information Report (TIR) 22 provides step-by-step actions for validation.
2006—O/K International provides Ethernet connectivity for capturing pouch sealing data from multiple machines to a PC.
2006—Van der Stahl Scientific offers the MS-451-PV sealer with integrated peel testing system for seal strength testing per ASTM F88; with Visual Inspection Unit (VIU) system for inspecting pouch seal topography.
2006--In shuttle tray sealers Algus Packaging and SCA Consumer Packaging feature matched seal die systems; Algus offers a push button power shuttle for moving the tool in and out of sealing station.
2008—PAC Machinery develops the Med Vac Plus medical pouch sealer with work surface height adjustment and shielding Lexan jaw cover.
2008—Belco Packaging Systems provides verified specifications for shuttle-style sealers enabling easier transfer of sealing fixtures to any other Belco machine of the same size and model.
2009—Alloyd Brands unveils updated Aergo 2 line of tray shuttle sealers with the Aergo 2 Max PS featuring a 42 % increase in sealing area, with autocycling power shuttles for moving the tools. The electrical control box is integrated into the machine to minimize width.
2010--Packworld USA develops the ‘Watch Dog’ system, a redundant sensing device and alarm system to futher enhance the internal TOSS technology controls.
2009—Doboy, Bosch Packaging Technology offers a control package with Allen Bradley Micrologix PLC as an option in its CBS DM medical grade continuous band sealer, and a new band break detection sytesm.
2010-- CMD Corporation introduces Intelligent Sealing Technology on converting machines for controlling all sealing parameters with real-time closed-loop controller adjustment.
2010--Sencorp White introduces a constant heat sealer/cutter for the medical packaging industry with a knife mechanism integrated parallel to the sealing bar, enabling a one-step process for sealing and removing excess material from the pouch.
2011—Plexpack (Emplex Bag Sealing Solutions) launches updated MPS700 rotary sealers with see-through Lexan cover for visual seal station inspection.
“Early on, there was no validation requirement, and not much in the way of sanitation standards. The same sealer we sold for food products was sold for medical applications. Increased involvement by the FDA—and the possibility of litigation—led to significant changes in process control and that in turn translated into validation requirements for medical band sealers,” says Ray Johnson, product manager, Bosch Packaging Technology.
“Sealers improved with increased emphasis in accurate controls and monitoring systems. Requirements have moved beyond the bare minimum to the very exacting standards of today. Most companies have enacted procedures that exceed those standards,” Johnson adds.
ISO 11607’s requirement that all processes be documented, including sealing, encouraged packagers to look to the machines for sealing process records. Quality control personnel became involved, driving a focus on data acquisition software. PLC controllers could be plugged into a PC for down loading cycle data.
Zed Industries Inc. would introduce on-board data printers for recording production data from the PLC for storing with samples as records of consistency. Packworld USA provided optional data logging with hard copy profile. And Van der Stahl Scientific offered an integrated printer with its seal check system for documenting each day’s results.
But industry questioned the need for extensive data acquisition. People wanted better machines, not data trails that added to machine costs and invited closer FDA examination in an audit.
“The market told us that engineers wanted data collection, but at the end of the day they didn’t want to pay for it and saw it as superfluous. Manufacturers are streamlining down to the essentials of what makes an easy-to-validate machine,” said Charles Webb in 2000, then medical device team leader at Van der Stahl Scientific/Fuji Impulse America.
“If your machine is calibrated and alarmed, it will tell you when you have a bad seal. Memorializing the data does nothing more than take up disk space,” observed Russ Perone in 2001, then national sales and marketing manager, Packaging Aids.
Continuous data acquisition posed a particular challenge in impulse sealing, where fluctuating temperature generated streams of data. “All that data became a headache for people to process in an easy to understand manner. Users were spending too much time and resources not related to productivity,” said Liston Brevard, president, Impulse Dynamics Inc. in 2003.
“The real interest now is to provide a well-built machine where you can calibrate the instruments and components to what they should be and use this information and seal strength tests to develop validation guidelines,” Brevard said.
The story of heat sealers is one of continuous improvement addressing the many variables of heat sealing. Machines feature controls on operators, more durable components, and control systems for managing difficult materials and package configurations.
“The creation of new and superior plastic films has increased the demand for precision control because the temperature window has in many cases become smaller,” said Charles Trillich, president, Packworld USA in 2000.
In 2002, Curt Larsen, then packaging consultant for DuPont Medical Packaging cited 10-to-15 degree temperature variations across the sealing platen as a concern.
“Such variation can cause sealing anomalies, such as extreme seal strength variations, incomplete seals, and tray seal flange warpage. It may also transparentize Tyvek, which does not negatively affect package integrity, but may affect the consistency or smoothness of the opening peel forces and affect the look of the package,” Larsen said.
On the converter side, temperature maintenance was an early focus in pouch converting machines, which feature sophisticated process management controls.
“Knowing that temperature, pressure, and time are the critical ingredients for making a seal, the initial focus was on controlling the temperature component. I remember a time when we were pretty excited to achieve ±10° F level of control on pouch and bag machines. Now we’re controlling to about ±2° F. This is all due to the need to ensure consistency and quality of the seals on medical device packaging,” says Edward Verkuilen, regional sales manager, CMD Corp.
In constant-heat bar sealers and impulse sealers, tray sealers, and band sealers, vendors introduced technology and methods to help ensure consistent sealer performance. Machines alarm, lock the control panel, or prevent feeding of the material when sealing trends out of spec. For data retrieval for machine validation, units featured external ports for plugging in calibrated meters to monitor the accuracy and repeatability of the sealing parameters.
“In a nut shell, the pieces of equipment are becoming simpler, faster, and more accurate,” said Thomas Misik, VP sales and marketing, Belco Packaging Systems Inc., in 2000.
Belco Packaging in 2002 featured sealers with four validation ports for mapping temperatures across its continuous heat seal bars. On its tray sealers, multiple thermocouples are incorporated into the platen, designed so as not to interfere with heat distribution.
In continuous rotary band sealers, Plexpack/Emplex Bag Sealing Solutions features programming to alert operators with audio and visual alarms, or shut off or reverse feed in the case of out-of-parameter conditions.
With the CBS DM band sealer, Bosch Packaging featured a wrinkle detection function with defect conditions reported at the operator interface and a machine stop when faults that affect the integrity of the seal are detected. Bosch Packaging introduced a 500-position encoder on its B-550 M sealer for more precision in the belt speed monitoring critical for compliant sealing.
“Bandsealers [have evolved as] specifically designed for clean room applications, with stainless steel construction, lubrication free components, and sealing techniques that reduce particulate generation,” Johnson says.
In converting equipment, Doyen Medipharm Inc. featured modular control for its four-side-seal machines with software that independently controls the infeed, cutoff, side seal, and cross seal functions.
In pushing for heat sealing process improvement, CMD Corp. introduced Intelligent Sealing Technology. IST controls the entire sealing process, self-correcting for sensed process deviations as data is fed back to the controller.
“IST not only looks at the temperature control aspect of sealing, but also provides unparalleled control over the force applied, and the time factor as well. Force control is to within 1.5% of set point, and real-time dwell time control literally ‘closed-the-loop’ on sealing system repeatability and reproducibility. Our systems monitor and adjust all parameters ‘on-the-fly’ for the most consistent control available on the market today,” says CMD’s Verkuilen.
Delta Industrial in 2004 introduced its Delta Mod-Tech Reciprocating Heat Seal Module that enables a wide variety of seal patterns and sizes. The technology enables longer dwell times and higher pressures compared with rotary heat sealing, with servo motor control for accurate and repeatable dwell and linear servo motors for accurately matching web speed. Delta was awarded its first patent on the technology in 2009.
Plexpack/Emplex addressed difficult to seal bags with its series MPS 7300, 7700 of validatable rotary sealers. The sealers double heat and cool capacity with two heater bars and two cooling bars for 60% more output.
Cost-conscious customers moving to uncoated Tyvek prompted Plexpack/Emplex in 2008 to offer cooling bar configurations for a wider variety of materials. An optional rubberized pressure roller applies pressure to the seal once it leaves the heating section. “This allows us to seal through the inconsistencies in the materials and make a better, peelable seal,” Lewitt said.
SencorpWhite assisted customers with issues sealing mono-layer LDPE bags in constant heat sealing, where visual anomalies are introduced to the still warm and fluid seal as it is pulled away from the heated die. Sencorp integrated a Teflon cloth apparatus that eases pouch extraction from the machine while giving the seal enough time to cool.
SencorpWhite developed a customizable program for its chamber sealers in which any combination of vacuum and/or flush steps can be programmed with dwell times so the customer can vacuum down or flush up in one large step or multiple smaller steps as their process requires. The customer can fine tune the draw down rate to control the rate of vacuum during vacuum steps.
“Customers can also program an accuracy level for the vacuum/flush set point during the programmed dwell time. Instead of the manufacturer dictating the accuracy of their system, this program enables the customer to balance speed and efficiency with the accuracy appropriate for their process,” says Lynne Barton, senior account executive—CereTek, SencorpWhite.
PLCs with touch screen HMIs have allowed simpler and more accurate and repeatable control. In replacing separate microprocessors dedicated to specific tasks, a PLC enables easier setting of seal parameters along with improved diagnostics.
“Three independent controls take up more space and require more wiring and more lines to hook up. With a PLC, you are saving on materials and labor, and you may be saving on the cost of the equipment,” Packaging Aids’s Perone said in 2001.
In 2009, Doboy, Bosch Packaging Technology, offered a control package with Allen Bradley Micrologix PLC as an option in its CBS DM medical-grade continuous band sealer. The PLC supports easier setting of seal parameters and manages recipe storage, data logging, and password protection. Machine performance values are denoted, stored, and retrieved through the interface.
“We have seen many of the larger medical device packagers moving to PLC-based systems simply because they have the ability to acquire data on the machine’s performance. Generally, customers are looking for reporting on fault conditions,” Johnson said that year.
In sealers using individual discrete controllers for time, temperature, and pressure with hard wire relay logic, the availability of upgrades and options is limited, says SencorpWhite’s Barton.
“PLCs have significantly enhanced the ability for sealers to be configured with advanced control items such as electronic pressure regulators, recipe storage, and data acquisition. PLCs have also enabled machinery manufacturers to offer in-line electronic checks before and after the seal has been applied, such as bar code scanners, imaging scanners, RFID, tool identification systems, and non-destructive seal inspections. Any non-compliant package or component can then be segregated for disposition per the company’s standard protocol,” Barton says.
Atlas Vac Machine was the first manufacturer to add PLC control to tray sealers in the early 1990s while working with Medtronic Inc. to improve sealer and sealing process control.
For sterile packaging of implantable products with shuttle-style sealers, Medtronic upgraded to PLC control for better accuracy and repeatability of sealing parameters. The company would further upgrade to Nelipak rotary-style sealers to better fit the current manufacturing process flow.
At Healthpack 2009, David Bohn, then principle packaging engineer at Medtronic, presented an improved method for developing and controlling the sealing process in medical blister package heat sealing technology. The method uses a force value (1b/in.²) instead of regulated compressed air measurement as the pressure parameter. This can be accomplished either by performing a periodic “pressure profile” on a sealer and developing regression equations to determine the input pressure needed to achieve the optimum sealing force, or by adding a load cell to the sealer design to monitor the force achieved during the sealing cycle, Bohn said.
“The force value can be applied as a universal pressure parameter on any sealer that is using that same combination of sealing variables and materials. The direct measurement method helps to reduce short and long term variability in the sealing process and thereby provides more consistent results from every sealing cycle,” Bohn reported.
“There have been two major improvements in heat sealer technology in the last few years. The first major improvement was implementing load cells into the sealer designs,” says Bohn, recently retired after 43 years in packaging with Medtronic.
“I feel this is important because it fits very well with the newer lb./in² methodology for controlling the sealing process and is equally valuable when using the older DOE-generated sealing parameter methodology that uses input pressure as the pressure parameter. The second major improvement was the introduction of an all-electric sealer design by Atlas Vac Machine, which I believe to be a revolutionary as well as an evolutionary development in sealer technology,” Bohn says.
As the use of load cells provides a means for direct measurement of the force values during sealing, almost all sealers are still controlled by regulated air pressure. “The all-electric sealer technology removes the inherent variation caused by using regulated air pressure to indirectly control the sealing process; rather instead, using a direct force measurement to control the pressure part of the sealing parameter set,” Bohn says.
THE PEOPLE FACTOR
Sealers minimize the potential for human mistakes with features that limit the influence of the operator. Password protection allows only supervisor access for setting changes; PLCs identify recipes; and graphical interfaces signal out-of-spec sealing.
Bosch Packaging and Plexpack/ Emplex introduced bag top guides as a physical reference in positioning the pouch and setting the seal location on rotary sealers.
“Sometimes customers don’t use the machines for their intended purpose and in some cases don’t even realize they are misusing the machine. It is worthwhile to invest in operators that take possession of the process,” said John Lewitt, VP sales, Plexpack/Emplex in 2011.
RF and bar code systems ensure the correct loading of tools and sealing recipes. In a Belco Packaging solution, operators use a blue tooth hand held bar code scanner to read a work order bar code containing the sealing information to auto populate the parameters into the controller.
Belco Packaging and Atlas Vac Machine provided sealing recipes coded to RF tags fixed to each tool. The tags are read by RF reader antenna in the sealing chamber when the fixture is shuttled in. If the fixture ID doesn’t match the recipe selected for sealing, the sealer will not cycle.
“Machine and tool inventories have increased at companies as a result of acquisitions. In environments where people are making a lot of changeovers, the system reduces machine downtime,” said Belco’s Misik.
Atlas Vac Machine offers an RFID system across all its sealers.
“You have operators that are only permitted to select the recipe, and load the tool. If the two don’t match, they can’t proceed with the sealing. [At companies where] multiple products and tools are converging on one sealer, this is a good way to prevent mix-ups,” said John Abraham, president, Atlas Vac Machine.
For faster error-free changeover, tools tagged with RF chips that auto load parameters as the tool is placed in the machine were featured in the Aergo 2 tray sealers from Alloyd Brands, Tegrant Corp. Alloyd in addition implemented the ATEX system that auto loads and unloads the heat plate.
The Aergo 2 debuted with optimized platen mass for better temperature uniformity and more heater wattage for faster recovery time and control of temperature loss. The units achieve a ±5% variation from set point across the surface.
Packagers and vendors have focused on accurately measuring the temperature of the sealing device at the point where it engages the work piece. Though machines can be evaluated with certified measuring devices, relying on machine self-monitoring as the final test of performance was held up as a concern.
“In most cases when you are validating temperature with validation ports, the same thermocouple that is supporting the temperature controller is supplying the output to the validation port. This begs the question: Are you validating the actual temperature of the sealing element or simply the accuracy of the signal the thermocouple is sending to both the controller and to the independent calibration meter?” said Trillich, president of TOSS Machine Components and Packworld USA in 2006.
Van der Stahl Scientific’s Webb would comment: “It is not good science to ask a machine to wholly monitor itself with watch dog equipment intrinsic in the machine.”
“The focus by many medical device manufacturers is to work with packaging machinery that has multiple alarm systems that are used as the arbitrators of whether or not the machine has engendered a good seal. This is effectively asking the barber if you need a haircut,” Webb says.
Seal strength testing—performed as a cornerstone of validation—needs to be systematically carried over to pouches in production, Webb argues.
Van der Stahl would coin the term “forced policy compliance systems” in introducing its MS 451 PV heat sealer with integrated peel-strength tester and VIU seal integrity inspection device. Operators are required to stop packaging at given intervals and perform a destructive tensile test. If the test does not meet the peel value requirement, the unit will not operate until intervention by a quality manager.
Impulse sealing is a challenging technology, as a variable dynamic process. When residual heat builds up in the band and bar mount as the sealers repeatedly cycle, the temperature set point is reached faster and faster. Temperature profile variances are created that need to be measured and controlled.
In 1997, PMP reported that “Impulse sealing has been cast aside by most medical packagers due to validation difficulties. The problem is temperature control.”
Vendors in the intervening years have responded with advanced technology. High-response controllers measure and respond in milliseconds as the sealing element heats and cools. Machines begin sealing only after the set point is attained. Incorporated PID algorithms anticipate temperature deviations in calculating the required heating input.
In the TOSS technology used in Packworld USA machines, a closed-loop controller measures the resistance change in a precision-made heat seal element, which directly corresponds to the element’s temperature. The controller constantly monitors the element temperature, adjusting supplied power to keep the temperature at set point.
“Thermocouples do not respond fast enough to capture the peak sealing temperature of the sealing band. New technology employed in impulse heat sealing can ensure a repeatable sealing cycle, while gripping the work piece until the seal is properly set,” Packworld’s Trillich said in 2002.
In 2005, Dana McDaniel, customer service manager, Packaging Aids, observed: “With impulse sealing you are getting a 3° variation from your set point, where with earlier machines it was swinging 15° to 25° above or below your sealing temperature.”
Aline Medical Packaging in 2006 introduced the PLC-controlled Precise Seal medical impulse sealer with PID software that reads and updates heating element power every 18 milliseconds, maintaining temperatures at ± 1° of the set point.
Impulse sealing is used in applications where the materials must remain clamped in place through the cool down period to ensure an optimal seal.
“Sealing a pouch is a molding process. You are liquefying the clear film and inducing it to flow into the fibrous back of the medical grade paper or Tyvek. Then you are setting it in place as the seal cools under pressure,” Van der Stahl Scientific’s Webb described.
Accu-Seal in 2005 developed an impulse sealer for peelable CryoLoc FEP pouches from CryoSystems that used a heating element with greater mass and addressed heat sink with a non heat absorbing band pad assembly. The heat was brought up slowly, for consistent heat delivery to the bag in a range high enough to get a good seal on the two-layer bags but not to cause the bag to stick to a disposable sterility barrier or cause the barrier to stick to the band.
Constant heat sealing remains a favored approach in many applications.
Multivac uses TOSS Machine Components’ TOSS technology in vacuum chamber machine pouch sealing as a safety feature that avoids the hazard of a constant heat bar. “A thermocouple used with an impulse seal element will not provide a consistent and repeatable temperature reading cycle after cycle. You have to capture the temperature at the point of contact with the sealing surface,” Bill Williams, product manager, Multivac, said in 2005.
Multivac uses constant heat sealers in its tray sealers and roll stock machines. “We have seen a lot of our customers go to solid heat bar units if their packaging does not require low residual oxygen, because they are easier to validate,” Williams said.
“Although SencorpWhite manufactures both impulse and constant heat sealers, we recommend the use of constant heat sealers for medical packaging applications where possible. We find that they are easier to calibrate and validate, and the maintenance costs are significantly lower,” says Barton.
Medical device packagers require mechanically reliable machines, and look for vendor support in areas such as IQ and OQ and trouble shooting of materials. As vendors have devised technology to ensure sealing consistency, they have sought to keep costs in check.
Process control has matured to include redundant monitoring, and packaging machines tied into plant wide data acquisition and SQC/SPC software programs.
“Modular platforms will enable packagers to retrofit sealers for new requirements, such as bar code scanners and RFID readers. Programs that can be easily updated in the field will permit packagers to quickly and efficiently modify software for new options and in-line inspection tools,” says SencorpWhite’s Barton.
“The recent UDI directive is causing machinery manufacturers to investigate ways that packaging equipment can be tied into the systems that will monitor/trace the disposition of a unique device throughout the manufacturing and packaging process and, ultimately, connect that system into the distribution channels for total traceability,” she adds.
Bosch Packaging offers printers, bar code readers, scanners, and reject systems, as the need for product identification has increased. Future sealers will have to be adaptable to changes in materials and offer elevated systems for data collection and disposition of non-compliant packages, says Bosch Packaging’s Johnson.
“Sealing technology is constantly evolving and is driven by changes to materials, equipment, and methodology,” says Medtronic’s Bohn. “All factors must work together to achieve an efficient and effective sealing process that is able to be reliably monitored and validated to the end result that the customers always get what they require.”