Heat Sealers Aim for Precision
Meeting standards for heat-seal packaging requires responsive technology, machine maintenance, and seal testing.
By David Vaczek
A custom heat seal press from Packworld USA provided Ethox International with a validatable machine for sealing and cutting a large device cover.
Medical device and drug packagers have sought heat-sealing technology that controls the sealing process and signals when process parameters drift out of range. Validatable machines support machine validation, whereas testing establishes statistical proof that sealing processes consistently yield a specific outcome.
ISO 11607 requires validated packaging processes for sealing sterile barrier systems. Critical parameters must be specified, monitored, and routinely documented to ensure that the machines are capable of delivering reproducible results.
Heat sealer providers have responded with control features and machine components designed to maintain consistent sealing values and thus ensure compliant seals.
Digital technology is more precise and easier to use than analog gauges. PLC-based sealers and systems controlled by PC-based software enable control and monitoring of packaging parameters, besides allowing programming flexibility.
For temperature control, PID (proportional-integral-derivative) controllers account for the history and rate of change of heaters to support tighter temperature control of hot bars and impulse sealer bands. Many sealers feature input and output ports for machine calibration or support for process monitoring and linking devices, such as printers and PCs, should automatic documentation be desired.
“With the PLC control offered on our sealers, we can provide programming flexibility and enable custom control options for the customer,” says Lynne Barton, marketing manager, Sencorp (Hyannis, MA). “You can have recipe storage for loading saved parameters, without the need to update the individual sealing values. This reduces the potential for error inherent in a system using discrete controls for each function.”
Facing package process validation requirements, packagers often look to heat sealer vendors for documentation to support the validation process.
“As a resource for customers looking for support with machine process validation, we perform test seals on all of our customers’ packages. People often don’t know where to start in defining their sealing parameters,” says Lesley Jensen, general manager, Accu-Seal (San Marcos, CA).
“For support with validation, we provide low, nominal, and high sealing parameters, as well as detailed specifications and operational instructions to simplify the ISO 11607 IQ, OQ, and PQ processes,” she adds.
Careful setting of sealing tolerances may be for naught if machines are not properly maintained. Seal strength testing provides a method for demonstrating that processes are in control. “Customers are searching for more user-friendly designs, for machines with modular components that are easy to maintain, and to extend the life of machine components,” Jensen says.
Hawo GmbH employs a PC-based heat-sealer control system to document critical sealing parameters.
AlloSource (Centennial, CO) uses Accu-Seal’s Model 730 medical impulse heat sealer for packaging bone and tissue allografts. Jeff Hubbard, process equipment specialist, says the sealers are calibrated annually and undergo quarterly preventive maintenance.
“In most cases after requalification or machine repair, we perform pull tests on numerous bags to confirm compliant seals.” Bags are sealed on the 20-in. bar at 2-in., 8-in., and 16-in. intervals, says Hubbard. AlloSource seals premade film-to-film and film-to-Tyvek pouches.
The Model 730 features PLC control for storing sealing recipes and parameter monitoring. Supervisors can use an access code for reprogramming. Audible and visual alarms require supervisor password override.
Packaging volume depends on donors, but it’s not uncommon for one machine to accomplish several hundred seals in a day. “The Accu-Seal sealers are high-quality machines, which—we have found—provide very consistent results,” says Hubbard.
To handle increased production at the Colorado plant, the nonprofit firm is increasing its Accu-Seal installation from 2 to 12 units. An AlloSource skin-graft packaging facility in Salt Lake City uses two of the sealers, and two are on order for a facility in Cincinnati, Hubbard says.
Reglera (Lakewood, CO) is contracted for machine validation services. “We will be proposing qualification by similarity. You require less time and data to validate machines when you are using the same machine from the same company,” Hubbard says.
Accvacs (San Diego) is upgrading impulse sealers with a PLC heat controller launched by Panasonic Electric Works Corp. of America (New Providence, NJ). The Impulse Heat Controller PLC is a compact 2 × 2 in., which makes it suitable for machines with space constraints.
Accvacs offers impulse heat sealers and vacuum sealers in widths of 10 to 35 in. For temperature control, the sealers use the Panasonic heat controller in combination with Accvacs’ Digital Smart Controls to produce repeatable, validated seals 100% of the time, says Tony Hernandez, president and founder.
“Using the Panasonic controller with our Digital Smart Controls, the customer can change machine processes without any programming knowledge. We send them an EPROM chip they plug in to reprogram the machine for five different operations,” Hernandez says.
Sidney Brooks, senior product specialist, Panasonic Electric Works, says that the Panasonic unit precisely controls heating and cooling processes to ensure compliant seals, with a temperature update time of 18 msec.
“In order to control the very fast heater in an impulse sealer, you need a fast update time of each temperature reading. With standard temperature controllers that update every 250 ms, there is a wide temperature gradient between readings. This makes it difficult to control the heating of the element,” says Brooks.
Panasonic Electric Works's impulse heat sealer features a temperature update time of 18 ms.
The Panasonic controller’s PID algorithm reads and responds to temperature input from the thermocouple every 10 msec. “The PID can be programmed to update temperature in just a few milliseconds. In order to get the full performance out of this device, the customer would require a thermocouple that is faster than 18 msec,” Brooks says.
A built-in, push-button Auto-Tune feature automatically configures PID set points by analyzing the thermal properties of system components. “Different heaters have different thermal properties, and different response times as a result. Auto-Tune ramps the heat up and turns it off multiple times, measuring the response times and temperature overshoot and generating a curve. The shape of the curve is analyzed for generating PID values that support fast and smooth controller response with no overshoot,” Brooks says.
The controller features “total machine control” capability with eight built-in digital input ports, five transistor output ports, and a relay output port, besides two communication ports for working with devices such as PCs and HMIs. For adding functions such as control of pressure and dwell, software can be written in ladder logic or use IEC 61131 programming software for downloading into the controller’s flash memory, Brooks says.
Ethox International (Buffalo, NY) uses a variety of heat sealers as a provider of contract manufacturing and sterilization services to medical device and pharmaceutical companies. The company manufactures and pouches a wide range of hospital products and offers laboratory testing services, including package integrity testing.
Continuous band sealers from Doboy Inc. (New Richmond, WI), APM (Ronkonkoma, NY), and Packrite (Racine WI) are used for some applications. Ethox employs six impulse sealers from PackworldUSA (Nazareth, PA) for film-to-film and Tyvek-to-film packaging of devices such as molded components, tubing assemblies, and tubing kits, says Mike Salvati, project engineer, Ethox.
“The Packworld sealers are used where the size and placement of the seals are more critical. We want to make sure that we have a 3¼8-in.-width seal on Tyvek-to-film pouches,” Salvati says.
The company sought new technology to meet a customer’s request for a device handle cover with a 42-in. length. “We tried it on a heated platen press, and it didn’t work. The platens and aluminum dies we have in-house were not large enough to weld something this long in one step,” he says.
Mutltivac's vacuum chamber sealers with constant heat sealtechnology feature Beckhoff Industrial PC control.
Ethox adopted a heat-seal press machine from PackworldUSA to handle the unique bag configuration. The unit features a 22 × 44-in. platen customized for sealing and die-cutting the large bag. One platen is fitted with the heat-seal band shaped to create the seal. The opposing platen with a resilient face conforms to the shape of the heat-seal band when the platens are forced together for impulse sealing. The unit features a horizontal sliding door for loading the blank and unloading the finished three-side-sealed piece.
The machine seals and cuts in one pass, avoiding the need for a separate trimming process that Ethox employs with the heated-platen press, Salvati says.
“The main reason we went with the PackwordUSA heat sealer [equipped with TOSS technology] was because of its validation capabilities. We can set limits and monitor the cycle on the HMI screen and record those values. Temperature readings for the heating and cool-down phases are constantly on display, with readings reported in milliseconds, without the delays we were seeing with thermocouple control on the heated platens,” says Salvati.
“The sealing is quicker, more accurate, and more precise. We are looking at a 3-second cycle time, as opposed to a 10- or 15-second cycle time with a heated-platen press,” he adds.
Salvati says that one consideration was the machine’s sealing force and electrical power capacity. Reserve capacity will support larger pattern shapes and planned applications where multiple smaller bags are made per cycle.
The heat-seal press is configured to deliver enough platen force and electrical power to effectively seal and cut two times the sealing surface that can reasonably be designed into a 22 × 44-in. platen, says Charles Trillich, president, PackworldUSA.
“The force applied to a jaw bar or platen in a heat sealer is a function of the air pressure supplied by the regulator, multiplied by the size and number of pneumatic cylinders employed. To ensure uniform platen-pressure distribution, the force must be delivered by a suitable number of adequately sized pneumatic cyclinders,” says Trillich.
Electrical power in the Ethox sealer is delivered with a 4.4 kVA transformer that is designed to ensure adequate power for other tasks that can be fitted on the platens.
Trillich notes that “electrical power has to be sufficient to achieve rapid temperature ramp-up and accurately maintain the sealing temperature across the entire heat-seal band for the duration of the sealing cycle.”
PackworldUSA offers heat-seal press machines in sizes ranging from 6 × 8-in. to 22 × 44-in. TOSS technology supports fast, accurate band-temperature control by foregoing the use of intermediate devices such as thermocouples and resistance temperature detectors for measuring band temperature.
“TOSS technology uses a calibrated heat-seal band that is itself the temperature-sensing means, with temperature monitored by a high-response controller that adjusts the power supplied every 16 milliseconds,” Trillich explains.
“Attempting to monitor temperature at any specific location on a band is fruitless because there is no assurance that the temperature at one location is uniform throughout the length or surface of the impulse-sealing element,” he says.
An algorithm calculates the amount of energy required to reach and maintain the preset temperature without overshoot. The controller signals the platens to release the piece when the predetermined cooling temperature is achieved.
“Because the temperature of the heat-seal band is precisely monitored, excessive heating is avoided, cooling is more rapid, productivity is increased, and validation is simplified,” Trillich says.
Multivac provides customers with documentation to assist with on-site IQ, OQ, and PQ.
Salvati says Ethox has sent samples of the bag to the customer, as it completes OQ and PQ on the sealer. “We have provided quotes to other customers for products that we would recommend to use this sealer, and we plan also to use it in some of our internal applications. If we get a purchase order for another project, we will be requesting another Packworld die.”
In vacuum chamber sealers, Multivac (Kansas City, MO) and Sencorp have developed sealers featuring constant heat seal technology.
Multivac has launched the C400 TC (Thermal Control) and C500 TC vacuum chamber machines. The single- and double-chamber heat sealers are controlled by an industrial PC (IPC) computer-based system that Multivac is deploying this year also for its tray sealer and rollstock machines.
“We have already seen significant demand for the C400 TC and C500 TC machines domestically, and companies’ international divisions in Europe and the UK are welcoming this technology,” says Bill Williams, product manager, compact packaging systems group for Multivac.
“Customers want assurance that packages are produced with compliant seals each and every cycle. We have successfully built validation packages for our clients using impulse sealing and will likely continue to do so. But there is legitimate debate in the industry about whether that technology is best suited for validation. The C400 TC and C500 TC sealers tightly control temperature, pressure, and dwell tolerances, giving customers the validation they need without the controversy. We also offer parts and service support through our worldwide network of offices,” says Williams.
The vacuum sealers feature zoned water cooling, employing a water jacket around the seal bar. This feature helps in the control of the bar temperature and addresses operator safety issues by preventing heat transfer to the machine’s outer surfaces, says Wil Caraballo, technical manager, Multivac.
The C400 TC and C500 TC sealers maintain a temperature window of ±2°C, sufficient for sealing a wide range of materials. “By using a well-regulated temperature-control system in conjunction with the mass and properties of the bar, we maintain a very accurate temperature across the seal area and across the entire seal bar,” says Caraballo.
PID LOOP CONTROL
Consistent temperature is maintained with a PID controller loop that logs the temperature of the bar, anticipates heat loss, and directs heating to compensate, minimizing cycle temperature variances. Two thermocouples monitor the bar temperature in a redundant approach: One controls the heating of the bar, and the other monitors the seal-bar temperature. If either probe exhibits temperatures outside of set parameters, the machine alarms out and shuts down. Thermocouples directly connect to thermocouple cards that convert the input into a digital signal that is understood by a Beckhoff IPC computer-based control system.
Caraballo says that the Beckhoff IPC computer-control system provides faster real-time reporting on heat-sealer process conditions, compared with most PLC-based systems. Through a touch screen interface or a remote PC linked by Ethernet, users can monitor and control critical process parameters, such as cycle times, incoming pressure, seal bar pressure, and chamber vacuum.
Multiple sealers can be networked for downloading data to servers for remote control and troubleshooting, such as through a secure Internet connection.
“In managing the heat sealer, we are using less than 5–10% of the available processing capacity. A user could add modules for controlling upstream or downstream equipment,” says Caraballo.
The validation package offered with the C400 TC and C500 TC models is prepared to help users comply with ISO 11607. Process data are stored for CFR 21 Part l l compliance and for accurate lot tracking in product recalls.
Multivac provides customers with documentation to assist with on-site IQ, OQ, and PQ.
Sealers are first calibrated and validated at the factory. “The utilities such as pressure, voltage, and temperature change when the machine is moved from our plant to the customer’s site. The ambient temperature will change in the production environment. Customers usually have a metrology department to perform final calibration with calibrated and certified instruments,” Caraballo says.
In establishing the machine’s operating window and setting the sealing parameters, users can set upper and lower acceptable parameter limits. Sound and light alarms signal any failure that shuts down the machine. The IPC control panel provides an error code with a description of the failure that is dated, time stamped, and recorded.
Sencorp will exhibit its 12-DDS/2 Deep Draw Vacuum Chamber Constant Heat Bar Sealer for the first time at the MD&M East show in June. The PLC-based unit features a touch screen at the front of the machine, with digital indicators for vacuum, gas flush, seal-die temperatures, seal pressure, and seal time. Pouches may be evacuated and flushed up to nine times before sealing.
“Customers are looking at the 12-DDS/2 to replace their current chamber sealer technologies. The sealer’s hot-bar technology supports high repeatability, ease of use, and low maintenance,” says Barton.
The sealer begins to cycle automatically after the pouch is loaded into the seal platform clamp and the lid is closed. The lid raises two inches after cycle completion to indicate the pouch is ready for unloading.
The seal bar features a heater cartridge with custom-designed watt density to maintain even heat across the seal area. Temperature is maintained with minimal fluctuation throughout a production run.
Sencorp can customize control options for the customer and reprogram the PLC EPROM and PID controller to custom specifications or when upgrades are available.
Software can be tailored to support bar code scanners and printers, says Barton.
“Upgrades and process parameter settings are handled much more easily with a PLC. The 12-DDS/2 PLC can be programmed for capturing data in a data-acquisition system, enabling the customer to build historical data files,” says Barton.
Sencorp tests all equipment prior to shipping, to document repeatability and accuracy with calibrated instruments, providing a certificate of calibration upon request.
“Most companies require that equipment be calibrated after installation at the final place of use, to confirm the machine can perform within the published specifications. They will often recalibrate if the machine is moved to another facility,” Barton says.
hawo GmbH (Obrigheim, Germany) offers new PC-based software for control and validation of its hm 3010/3020 DC-V and hm 3010 DC-VI rotary sealers. hs 3000 PC software is installed on an external PC linked to the sealer via an RS-232 or universal serial bus interface or Bluetooth wireless personal-area network. The software includes modules for device control, text control, and process control. Up to 2500 text entries can be made for text transfer to and from the sealer.
Christian Wolf, managing director, hawo GmbH, says that the PC-based system supports easier input, viewing, and control of data. Data are delivered continuously to the software, documenting that critical sealing parameters correspond with set parameters. The software can document input from bar code readers.
“Critical parameters in packaging processes have to be continuously monitored and documented to comply with ISO 11607 Part II. For companies that are only now starting to validate their processes, we recommend documentation software that automates and simplifies the monitoring process,” says Wolf.
PID controllers used in continuous-band sealers and hot-air sealers manufactured by Fischbein-Saxon Inc. (Statesville, NC) can be programmed to shut the units down if preset sealing temperatures aren’t reached. Customers use tachometers to validate belt speeds. Transducer signals confirm crimp wheel compression. “We test our units with customers’ bags or pouches at the factory to establish sealing parameters before users validate on-site,” says Garry Jones, export sales manager for Canada and Mexico.
Typical medical customers of continuous sealers produce 40 to 50 bags per minute.
In continuous hot-air sealing, the air is forced through a series of manifolds and around temperature-controlled heating elements. The hot air is directed in a precise pattern to the front and backside of the sealing area. Using the PID temperature controllers, the operator establishes the correct sealing point. Sealing temperatures can be held at ±1 to 2°, says Jones.
“The band sealer produces the smoothest, most attractive seal you can get. Hot-air sealers are most often used in business-to-business applications where there is less emphasis on the package aesthetics,” Jones says.