Heat Sealers: Measuring Heat Sealers
By David Vaczek, Senior Editor
Cryo Systems is using a heat sealer from the Accu-Seal for its cryongenic materials.
Heat sealers have improved significantly in recent years. Machines can now more precisely control sealing parameters, and therefore produce quality seals, more consistently. Controls for monitoring and reporting, as well as fail-safe alarms, provide assurance that functions of temperature, pressure, dwell time, and speed are held within range and can be validated.
These improvements don’t mean that medical device manufacturers are resting easy. Machine performance has to be adapted to new materials and packaging systems. And companies upgrading heat sealer technology must test its performance with their packaging and ensure that they are meeting standards for installation, operation, and performance.
Those standards are currently being updated. An ISO working group (ISO TC 198, WG7) has completed the newest revision of ANSI/AAMI/ISO 11607, “Packaging for Terminally Sterilized Medical Devices.” The guidance document sets out requirements for materials, package design, testing, and manufacturing processes. Member countries are in final balloting on the new document, which harmonizes ISO 11607 with EN 868, “Packaging Materials and Systems for Medical Devices Which Are to Be Sterilized, Part 1, General Requirements and Test Methods.”
“It is a substantial rewrite,” says John Spitzley, cochairman of the U.S. ISO working group and a technical fellow with the Spartan Group (Hudson, WI).
The document sets out the package development process in an easier-to-read fashion. It is divided into two parts: materials and package design, and validation requirements for manufacturing processes. “The information is presented much more comprehensively, and as a linear process that people can follow,” he says.
In addition, it incorporates European CEN standards into the ISO standard. “Now there is one standard. If you comply with 11607, you are complying with CEN. This will make doing business internationally much easier,” says Spitzley.
User demands for heat sealers vary widely. “One wants speed. Another wants more controllers for validating, though more controllers make validation a longer process. Customers requiring extra validation are often doing it because of liability or a product recall in their past. A customer may want an easy setup to be up and running in a week. One of our customers paid a premium to have the product delivered two weeks quicker,” says John Lewitt, vice president of sales, Emplex Bag Sealing Solutions, a division of PlexPack (Toronto).
Avid Medical (Toano, VA) sought more-precise control and monitoring of temperature, pressure, and speed for sealing poly bags with Emplex’s MPS 6700 continuous rotary-band sealer.
“Our seal quality has always been passable. We needed a machine that was easier to use and offered more- precise control and digital reporting for validation,” says Dean Fisher, director of production, Avid Medical.
The machine is fail-safe in the sense that if the sealing falls out of parameters, operators are notified with audio and visual alarms, and a reverse-feed function stops the process. If the bag passes through completely, it has been sealed at the set parameters and it has been validated, says Fisher.
The MPS 6700 features a conveyor line that is synched electronically with the sealer and is monitored by a digital tachometer. A popular configuration is a unit that uses an 8-ft-long, 24-in.-wide horizontal system geared for sealing large products lying on their sides, says Lewitt.
“We have sold dozens of these horizontal systems for packaging medical kits. This is a market that has really taken off. I have been told by a couple of customers that their business has expanded due to the increased military actions around the world,” says Lewitt.
Emplex is offering different cooling-bar configurations to improve seal appearance without compromising the seal, for poly, foil, and Tyvek bags. “Our standard cooling-bar configuration used to seal everything. But now we are seeing extreme variations of materials in the marketplace. A lot of cost-conscious medical device start-up companies are looking for lower-cost products.
Converters are providing them with [new] Tyvek blends, and we have had to respond in kind. People don’t blink at the $750 for our Tyvek option, because of the savings when they use the more-economical uncoated bags,” says Lewitt.
|Emplex’s MPS 6700 is being used for medical kits.|
Impulse sealers have become more widely used in medical packaging as their technology has improved. Temperature control can be a particular challenge with impulse sealers, as controllers must read and respond in microseconds to the high-speed heating and cooling that occurs each cycle in the sealer band.
“The tolerances have become closer and the performance more consistent, particularly in the temperature control,” says Dana McDaniel, customer service manager, Packaging Aids (San Rafael, CA.) “With impulse sealing, you are getting a 3-degree variation from your set point, where with earlier machines it was swinging 15 or 25 degrees above or below your sealing temperature,” says McDaniel.
Continuous-band and constant-heat sealers are often requested by medical packagers because they provide high-capacity output. Continuous-band and constant-heat sealers are typically used when output is 15 bags or more a minute.
“You have to look at the materials you are sealing and whether you need peelable or nonpeelable seals. The majority of medical device packagers creating peelable seals are using constant-heat jaw sealers that do not impart a cooling cycle under pressure,” says Donald Barcan, president and CEO, Donbar Industries Inc. (Long Valley, NJ), a package engineering consulting firm.
All Packaging Machinery Corp. (Ronkonkoma, NY) has launched a continuous-band validatable sealer (Model VBS-DH-3/8-10-V) with a self-contained air compressor for portability, and quad digital temperature controls. Four independent closed-loop digital temperature controllers using dual-point thermocouples regulate and monitor its four heating bars.
“This sealer can seal Tyvek at a rate of 40 ft/min, or 40 packages 6 in. wide with a 6 in. gap between them,” says Daniel Wood, vice president of manufacturing for All Packaging Machinery.
“If customers need to produce a large quantity of pouches, the band sealer is preferred. With an impulse sealer, you need to wait for the machine to cycle and for the jaw to release. You are sealing six to ten packages per minute, maximum,” Wood says.
ADDRESSING SEAL QUALITY
Medtronic Inc.’s CRM business (Minneapolis) has progressively upgraded the blister pack sealers it uses for sterile packaging of its implantable products, including defibrillators, pacemakers, and pacing leads. It upgraded to shuttle-type sealers with PLCs (programmable logic controllers) providing better control over parameters and tolerances. The company is presently phasing out the shuttle machines in favor of four-position rotary sealers from Nelipak BV (Netherlands), which offer advantages including even better pressure control, says Dave Bohn, principal packaging engineer, Medtronic.
|Vacuum-chamber sealing is often used for modified-atmosphere packaging. Photo courtesy Multivac.|
In the early 1990s, “We were getting variability in our seals because we were unable to adequately control our sealing parameters. We made a wish list that turned into a specification, and we found a manufacturer to build a PLC-controlled shuttle-style machine to meet our requirements,” he says.
The sealer with the PLC provided tighter control and monitoring of parameters and tolerances, allowing more accuracy and repeatability in pressure, temperature, and dwell time. On the old machine, dwell time was set using a dial with indications in increments of 11¼2 seconds, making it hard to accurately read and set that parameter. “You didn’t know exactly where the dwell was,” he says. The PLC allows digital accuracy to a tenth of a second.
“The accuracy of the air pressure regulator gauge used to control the sealing pressure on our old machines was at best vague, as we set and reset the pressure for different products. The PLC machine offered much more accurate and repeatable settings, allowed for setting upper and lower tolerances, and included alarms when faults were detected,” he says.
“With temperature, we set it and hoped it worked for the process we were doing.
It might be adequate for one or two sealing cycles a minute, but if we were sealing 10 to 15 packages per minute, we didn’t know how fast we were pulling heat out of the hot plate, and how quickly the temperature loss was being sensed and replenished by the heating platen,” says Bohn.
The PLC sealer addresses the issue of the difference in temperature between the heating platen, where the temperature is monitored and controlled by the PLC, and the sealing surface of the hot plate. The sealing surface temperature can be 5 to 10 degrees less than the temperature indicated for the platen. Medtronic identifies and programs an offset temperature into the PLC to achieve the temperature at which it wants to seal.
“We obtain a one-to-one comparison between the PLC monitor and the hot-plate temperature,” says Bohn. “We looked at using an infrared pyrometer to monitor the surface temperature, but the accuracy wasn’t what we needed it to be.”
Removable temperature probes were used at the seal area immediately after sealing to see how effectively the controller was staying within range and how much heat was being delivered at the seal.
Even with the new shuttle-type machine, Medtronic discovered that the pressure control was not as good as it needed to be. “We found that there was significant variation from cycle to cycle in the downforce yield at a constant input pressure, and that the downforce yield was not equivalent from one machine to another at the same input pressure,” he says.
To normalize one machine to the next, Bohn did a pressure profile on each machine. He used those data to determine how much input pressure was needed on each machine to achieve a desired downforce yield. Sealing parameters developed on one machine could then be transferred to another.
The company gains added advantages with the Nelipak rotary machines. “The Nelipak’s pressure control and monitoring system is significantly better than that of our shuttle sealers, and machine variability is much better. We are expanding our use of them,” Bohn says.
Accu-Seal (San Marcos, CA) focused on improving machine thermodynamics when developing an impulse sealer for fluorinated ethylene propylene (FEP) cryo bags and sterile barrier products by Cryo Systems (Norfolk, VA) for sterile presentation in hospital operating rooms.
Cryo bags are used for the cryogenic preserving of cells and tissues. Among FEP’s properties are that it stays totally flexible in liquid nitrogen. Cryo Systems sources FEP from DuPont, which sells its Teflon brand, and Saint-Gobain Performance Plastics, a unit of Saint-Gobain Ceramics and Plastics Inc., says Kimber Burley, director of the Cryo Systems unit at Cryo Systems.
FEP requires high sealing temperatures, near the point of material destruction, held in a narrow range. For its peelable CryoLoc FEP pouches, which are patent pending, Cryo Systems sought to reduce the band sealing temperatures while ensuring that enough heat was reaching the bags.
Temperature had to be reduced from the usual 650ÞF at 10 seconds for FEP sealing to a 580Þ to 585ÞF range. This was done to prevent the bag from sticking to a disposable sterility barrier Cryo Systems has developed, and to keep the barrier from sticking to the band.
“The challenge was that at those temperatures, you couldn’t get a seal. There were too many barriers, including the sterility barrier, and two layers of FEP,” says Burley.
“We needed to get that heat to the bag more efficiently and consistently, in a more uniform manner. When you have a product that is worth $10,000, you cannot afford to lose one bag,” Burley says.
HEAT SINK CONTROL
In the high-temperature sealer for Cryo Systems, Accu-Seal replaced a T-profile band with a thicker quarter-inch flat band that supports more-consistent rise times as well as improves the seal’s uniformity and appearance. Heat is brought up more slowly, so it takes two or three times longer, about six seconds, to reach temperature. This ensures that the heat permeates through the sterility barrier and the bag layers. It used a non-heat-absorbing band pad assembly to address heat sink, concentrating heat in the sealing surface. In addition, the thermocouple is located under the band at the point of sealing.
“We found a way to build an element that has more mass, so you have a better idea of what is going on relative to the bag. We have found better ways to avoid heat sink into other parts of the machine,” says Tom Boyle, design engineer, Accu-Seal.
“Our focus was on machine thermodynamics. If you can’t get the energy into the bag at the right time and under the right pressure, then your seal is going to suffer, even if you have a highly-responsive controller,” Boyle says.
CONTROL AND VALIDATION
Multivac Inc. (Kansas City, MO) uses TOSS (The Optimum Sealing System) technology by Toss Machine Components (Nazareth, PA) to control and validate temperature and seal time in vacuum-chamber-machine sealing.
Multivac is vacuum-chamber-sealing preformed three-sided vacuum pouches of metalized foil or laminated film, some with Tyvek headers. Most of the applications are for medical devices that require modified-atmosphere packaging.
“We know that we are not only getting a good seal, but that we are sealing at the right temperature for those materials,” says Bill Williams, product manager, Multivac.
|Multivac’s vacuum-chamber machine uses TOSS technology to control heat sealing.|
TOSS provides instantaneous feedback on band temperature by measuring the fluctuating electrical resistance of the band, foregoing the use of a thermocouple for temperature measurement. The electrical resistance, measured by the controller at 60 times a second, directly corresponds to the temperature. In calculating the temperature coefficient of resistance (TCR), the controller derives an average band temperature and adjusts power accordingly to heat the band to the set point. The controller and band technology allow even heating across the band.
“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 because that is where you are sealing the pouch,” says Williams.
Multivac uses constant-heat solid-bar sealers in its rollstock and tray sealer machines. The company uses impulse sealing with the vacuum- chamber machines for safety reasons, for products requiring the vacuum and gas-flushing procedure to produce low residual oxygen in packages. Constant-heat bars in a vacuum-chamber machine could be hazardous if operators were to touch the bars,” says Williams.
“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,” he says.
Packworld USA (Nazareth, PA) uses TOSS technology exclusively in its line of validatable impulse heat sealers. “Accurately controlling the temperature of the heat-sealing element throughout the entire heat-sealing cycle, including temperature rise, dwell time, and cool down, is vital to achieving the optimum seal,” says Jeff Quinto, general manager for Packworld USA.
“Besides being able to precisely control the temperature of the heat-seal band on each and every cycle, another important factor to our customers is temperature consistency from one band to the next, and from one machine to another. Since TOSS technology uses the heat-seal band’s resistance to energy as the means of controlling its temperature, one can be assured that regardless of the band or the machine, the temperature will always be the same,” he says.
“Once you understand the costs associated with validation coupled with the cost of quality, you can then easily understand the extreme importance of precise temperature controls, as well as the need for machine-to-machine consistency,” he says.
Packaging Aids has experienced growth in demand for modified-atmosphere packaging, such as for sterile devices that degrade if exposed to oxygen. The demand has spurred sales of its MedVac line. “And there has been consistent demand for lower-cost equipment from start-up companies,” says McDaniel.
“We can offer them tabletop machines at 60% or 70% of the price of a floor model, with, depending on the material to be sealed, two-thirds or three-quarters of the production rate,” he says.