Pouch Sealing Technology Comparison Webinar
So, we’re going to go ahead and get started. I hope everyone can hear me all right. And thank you everyone for joining today. I see we have some familiar names on the list. It’s good to reconnect with everyone. I’m really looking forward to seeing you in person soon. So, hopefully we’ll run into each other at some trade shows or industry events. I’m pretty excited to get started, but just wanted to share a little bit about my background. And for those of you who don’t know me, my name is Lynne Barton.
I’ve worked at SencorpWhite for 21 years, and have steadily worked my way through the ranks to my current position as the Manager of the CeraTek Sales Department. I also serve on IoPP New England, and on AAMI. In my spare time, I’m a Girl Scout Troop Leader to 12 wonderful 10-year-old girls, two of whom are my twin daughters. I’ve been married for almost 22 years. And I just have to say, this photo of me is at least 10 years old, but I’m not going to update it until my marketing team forces me to.
So, enough about me, let’s get onto the interesting stuff. I just want to say that we have a lot of material to cover, so in the interest of time, I’m going to go through all of the slides and then we’ll field questions at the end, and go ahead and feel free to chat in your questions and we’ll loop back around to them later.
So, let’s get started. The most common type of pouch-sealing technologies used in the medical device industry include impulse sealers, constant heat sealers, rotary band sealers, and form/fill/seal machines. Now, this is not intended to be a completely exhaustive list, because there are some… shall we say more fringe technologies, but these are what are most commonly used in the typical technologies used today.
So we’re going to evaluate each one of these technologies individually to explain how they deliver and control process parameters, determine their best use for particular sterile packaging applications, and review the pros and cons of each type. So, I’m just going to preface this presentation with this thought, there is no perfect sealer for every application or scenario. Depending on your requirements, one may benefit you far more than the others, and that’s where hopefully this webinar will provide some guidance and value. But no matter what technology is used, the ability to properly program set points and alarm parameters to accurately control the machine should always be a necessity.
All of the machines we’re evaluating today have one job, to create a hermetic seal. Meaning that they have to create a barrier that prevents the passage of gases, liquids, and microbes from passing through the applied seal. And there are three critical elements to creating a hermetic seal, and one is to apply a specific temperature to a pouch for a certain amount of time or at a certain speed depending on the technology, and then with a certain amount of pressure or force.
So of these, temperature is the element that creates the greatest challenge. So, we’re going to be focusing on that for the majority of this webinar, and we’ll address time and pressure at the end, but first let’s grapple with that hot potato of temperature.
So, we’re going to start with impulse heat sealers. And when we talk about impulse heat, what do we mean? Merriam-Webster defines impulse with a very human slant rather than with a mechanical perspective. But basically, impulse is defined as a stimulus to action. There are some keyboards I want to pick out of these definitions that will help us understand what an impulse heat sealer is doing.
Impulse heat is the sudden act of driving toward an end result, in this case, a set point temperature. So, when an operator starts a cycle, the sealing die suddenly drives from ambient room temperature to set point temperature. This crack quick ramp up from a lower temperature to a higher temperature, requires the system to be designed for quick response. For that reason, the element creating the heat is usually a very thin nichrome wire. The small mass of the nichrome wire allows the die to heat up and cool down relatively very quickly.
So, this is a representation of a heat seal wave for an impulse heat sealer. When we look at an impulse sealer cycle, we start off at ambient temperature and we ramp up very quickly to set point. We dwell at that temperature for the programmed amount of time, and then we cool off to a release temperature or after a programmed amount of cool down time. At that point, our jaw opens usually before we’ve completely cooled off to ambient. And then we have our takt time between cycles.
This process occurs with every cycle. So, the repeating pattern looks something like this. An important note here is that in order for the process to be 100% repeatable, the sealer has to have enough time to completely cool off so that subsequent cycles start at the same temperature point as the first cycle. The implication is that if you’re trying to ramp up your throughput by shortening that cool down time, your next cycle will start at a temperature slightly warmer than the previous cycle, changing your process.
And before we go too much further into the pros and cons or considerations for impulse heat systems, let’s zoom in on that dwell time so we can see what’s actually happening during that process. To generate heat, a current is applied to a wire on the sealing die. This current is either on or off. So the current turns on when the system reads that the temperature is below the set point and turns off when the system reads that the temperature has exceeded the set point.
Impulse heat systems don’t employ a PID temperature control loop, and I’ll explain PID in a little more detail later, but so they don’t use a PID temperature control loop to control to a set point. Impulse heat systems respond extremely rapidly to control around a set point.
So, now we know what’s going on with the impulse heat, let’s take a look at some pros and cons for this type of system. There are a number of reasons why impulse heat sealers could be ideal for a particular packaging application. First, they are ready immediately. There’s no warm up time or stabilization time. From an efficiency standpoint, this is a huge selling point. Impulse heat sealers because of their comparatively lighter duty heating source are usually the most affordable sealing technology and have the smallest footprint.
Among the manual sealing technologies, they require the least amount of head space, both above the seal and below the seal. And since most machines are not guarded, this allows the operator to have full visibility of the seal area to see how the pouch is being presented to the sealing die. The product could be pretty close to the top of the pouch without having to worry about whether or not any guarding is going to interfere with loading it into the sealer. So for these reasons, impulse sealers allow the pouch size to be optimized for the product dimensions without a lot of consideration for how that will interface with the machine.
Now, from a material standpoint, they excel at creating weld seals on monolayer materials such as linear low-density polyethylene bags, like this one. LLDPE bags or header bags, where the final seal is made on the film-film end, are most easily processed on impulse heat sealers because of the cool downtime under pressure. This allows the materials to go from sort of a sticky flow state, which is required to be able to melt those layers together, to a stable solidified state before the jaw opens. And they are the only technology for high heat applications, which is usually a requirement for tissue banks, who typically use Teflon-based packaging materials.
From a material standpoint, impulse heat sealers can successfully seal pretty much any heat sealable material, but there are also some considerations for material interactions on impulse heat sealers to be aware of. Because of their inherent ramp up and cool down period, required for each cycle, Impulse heat sealers will always have the longest cycle time and provide the lowest throughput. Now, that does not necessarily need to translate to a negative. If you don’t require a high throughput but you want a sealer that offers great material processing flexibility, impulse heat sealers could be your machine of choice.
One common press design employed in impulse heat sealer technology more than any other is Cantilever Presses. Cantilever Presses can result in uneven pressure if they are not set up properly, or if you’re changing over to a different lot run which has pouches with a different material thickness. A Cantilever Press is parallel at just one point in the arc of movement. So, if the sealer is set up for a thinner pouch and then a thicker pouch is put into the seal area, the press will be out of parallel at the point that it engages the pouch.
We talked about the importance of ensuring the sealer has as time to return to a steady state between cycles so that subsequent cycles start at the same temperature as previous cycles. So, as production increases, residual heat builds up in the dies between cycles even if you have water pooling. As the residual temperature of the die increases, it also begins to act as less of a heat sink, which results in more heat energy being transferred into the pouch with every cycle. If the cooling cycle is programmed to release at a specific temperature, the total cycle time will also increase.
Seal strength and appearance of pouch materials will change over time as production rates and operator rhythms vary making validating a process and proving repeatability a significant challenge. This is critical for Tyvek applications because a buildup of heat in the seal area can cause the Tyvek to become overheated resulting in trans-prioritization or over-processing of the Tyvek.
Lastly, if you’re using an impulse heat sealer for sealing metalized foil it’s imperative that the Teflon cloth covering the nichrome wire is inspected frequently and changed out regularly. If the Teflon cloth is allowed to wear resulting in voids in the cloth, the current that is being pulsed through the nichrome wire can transfer to the metalized foil pouch, which more often than not is being held by an operator.
Now, I know this image shows an example of static electricity, but just work with me here, because he’s really, really cute. Anyway, the current that is passed from the nichrome wire to the pouch, and then to the operator, if they’re holding it, is usually not high enough to cause a healthy person any harm, but if that operator has an implanted electrical device, then there’s a chance that the current could disrupt that device.
So, the way in which an impulse heat system controls temperature could be achieved one of two ways. Most commonly, thermocouple-based systems are used, and then less commonly current resistance-based systems. For thermocouple-based control systems, the thermocouple must be extremely fine so that it can respond rapidly to the sudden change in temperature. Thermocouple placement is critical to ensure an accurate reading as the wire temperature profile can be as high as plus or minus 20 degrees Fahrenheit along the length, and plus or minus five degrees Fahrenheit across the width.
Because of the small mass of the nichrome wire, even a very fine thermocouple can act as a heat sink, causing a cool spot on the wire and consequently a visual imperfection in the seal. Regardless of the response rate of the thermocouple, for thermocouple-based system, the temperature is climbing so rapidly that it will always overshoot before the control system has time to respond and turn off the current.
For current resistance-based systems, the resistance is measured and then correlated mathematically to a temperature. The operator enters in a temperature set point and the system reports back the actual temperature, but it’s not really reading temperature, it’s measuring resistance and adjusting the current to deliver the desired temperature based on the calculation. And this method of controlling the temperature is extremely accurate and the overshoot is relatively much smaller than with thermocouple-based systems.
One of the biggest challenges for current resistance-based sealers is ensuring the system is properly calibrated for the particular wire material that’s used, and that the material has been stabilized. So stabilizing the materials is achieved by a process called burning in, so that the resistance of the wire does not change over time. Burning in is the process of applying so much heat so rapidly that it basically shocks the wire into a stable state.
So, burning in is not required for thermocouple-based systems, because you’re reading the surface temperature of the wire. And if the resistance changes over time, the temperature change will be read by the thermocouple and will report that back to the control system.
Using nichrome wires that do not have copper coated ends can result in a phenomenon called hot end syndrome. The ends of the die can become overheated and that excess heat can over time migrate into the usable seal area. So to prevent this from happening, selecting a nichrome wire that has copper coated ends is a best practice.
Ultimately, one of the greatest concerns for current resistance-based systems in sterile packaging applications is the fact that there is nothing to verify the surface temperature of the sealing die. So, if during maintenance the burning in process is accidentally overlooked, the results of the temperature in the sealing area is significantly affected without any feedback to the control system to indicate to the operator that there’s an issue. So, from a maintenance standpoint, because of the wear and tear sustained from heating up and cooling down with every cycle, impulse heat sealers require frequent maintenance, and replacing the nichrome band requires many requalification, because you are essentially replacing the heater.
So, that covers the challenges. We’ll move on to constant heat sealers. And I hope some of you are chatting in some questions. So this is, just like we did with impulse, this is a representation of a startup wave or power on heat up pattern for a constant heat sealer. So, when we look at a constant heat sealer heat wave form, we start off at ambient temperature and ramp very slowly to the set point. But then we stay very stable at temperature for the entire amount of time that the sealer is programmed at that temperature set point.
So, just like we did for impulse heat sealers, let’s take a zoomed in look at what’s going on during the dwell time for a constant heat sealer. And my clicks are not catching up with me. There we go. Due to the use of PID in constant heat sealers, and PID is an acronym for proportional integral derivative, which I will explain, the temperature system for a constant heat sealer is very stable.
PID control provides a continuous output with closed loop feedback to accurately control the process, removing oscillation and increasing process efficiency. So, kind of keep in mind this graph as we talk about PID and kind of take into consideration we’ve got that little bump up initially over our setting and then we kind of waffle a little bit and then it levels off. So kind of keep that in mind as we go through this slide.
So, when we talk about PID control continuous output closed loop feedback to remove oscillation, how is it doing this? Proportional or the P in PID gives an output that is proportional to the difference between the set point temperature and the actual temperature. It’s always trying to get to set point as quickly and efficiently as possible. As a result on its own, it will oscillate and never actually reach steady state. It’s always aggressively zooming right past that set point.
We have to temper this first trying to get to set point using integral value to limit that need for speed. Integral or I, calculates how far the actual temperature deviates from the set point. So when we’re first warming up and we overshoot that set point, like we saw on that graph, by a certain margin, then the I value calculates that error, how much did it go over? And the P value is trying to get as quickly as possible back to that set point, so it kind of goes back down again. And it’s fluctuating over and under that set point, the I value is calculating how much the temperature is deviating from the set point. Every time it goes past it, over a period of time to eliminate the error.
This algorithm continues with the I value recalculating the error until the error reaches zero and we’re at steady state. So again, thinking back to that graph. But the I value doesn’t have the capability to predict future behavior, it operates strictly on historical data. So that’s where the derivative or the D portion of this comes in.
Derivative or D anticipates the future behavior of the error. Its output depends on the rate of change of the error with respect to time, and it gives a kickstart for the output thereby increasing the system response. As a result, by combining these three controllers, we can get to the desired response for the system. Now, since we understand what each value does for a temperature control system, we can change the behavior of a system to meet a specific performance requirement by changing the P, or the I, or the D values. And this allows us to optimize the response system of a PID controlled heater.
So, as the operator cycles the machine and the temperature starts to deviate from the set point, the PID responds to the rate of heat loss. If the temperature is suddenly and dramatically pulled out of the sealing die, the PID responds with a higher percentage of heat output. As the sealer is cycled in a repeatable fashion, the PID can then predictively respond calling for the appropriate amount of heat to keep pace with the amount of heat being drawn out of the system, thereby keeping the temperature as stable as possible. And thinking back to that graph, that’s where it kind of levels off. But what happens when the sealer is not cycled in a repeatable fashion?
So, since it’s still a mechanical responsive system, inconsistent cycling makes it harder for the PID to keep the sealing die at a steady state. So, if an operator is cycling them… That’s me. It’s probably more like my evil twin. So anyway, our evil twin here is cycling quickly and then suddenly stops. It takes a few seconds for the PID control loop to respond to the fact that the heat is not continuing to be drawn out of the sealing die at the predicted rate and it will temporarily overshoot.
Alternatively, if the sealer is sitting idle and then the machine is suddenly cycled repeatedly at a high cycle rate, it also takes some time for the PID control system to calculate the rate of heat loss and respond with the appropriate amount of heat output. That PID pattern might look something like this. So, we’re settled and at nice steady state in the very beginning there. Our process value or the blue PV line is sitting nice and even with our set point or SP line, which is the green line. Our control output or CO line in red, isn’t doing much of anything because everything’s kosher.
Then we see that dip, and heat is drawn out of our sealing die and our process value drops. So our PID temperature control system responds by increasing our control output until the process value is once again at set point. Now, we are continuing to cycle at that same rate, and heat is continuing to be drawn out at the same rate. So our control output levels off a little bit, but it’s not trying to gain temperature, it’s still at a higher rate because we’re continuing to use heat at a higher rate, so that’s why this graph looks like it does. The red line ramps up and then stays at that higher level, because we’re continuing to cycle.
So, let’s take a look at a real world example of a sudden change in cycle frequency with a constant heat sealer. And this is a real temperature trending graph from one of our constant heat sealers. So, at the beginning there, we’re sitting idle at steady state, and then we start cycling at a rate of one cycle per second. So, the top green line shows our solenoid firing, and the second line down, which is our yellow line, is our proximity sensor confirming the sealing die is physically closed. Now, the third line down, which is pink, shows our process value. And the next line down is our control output. Lastly, that bottom graph is our SSR or solid state relay.
So here you can see actual data points for how the PID keeps a process value at or close to the set point. So as a result, like I’d mentioned before, the difference between impulse and constant heat sealers is that impulse heat sealers are trying to control around a set point while constant heat sealers are controlling to a set point.
So, now we know what’s going on inside a constant heat sealer, let’s get to some of those pros, cons, and considerations. Constant heat sealers utilize a cartridge that is either sandwiched or encapsulated by an aluminum sealing die. The cartridge heats up the large die mass, which you can see here, which remains very stable at the set point temperature. The effects of environment, including airflow or operator cycle rate, et cetera, have minimal effect on the temperature of the die because it takes a relatively significant influence to change the temperature of that larger die mass. So for this reason, temperature stability on constant heat sealers is unparalleled.
All constant heat sealers are thermocouple-based. And the thermocouple is placed near the seal surface, but not on the seal surface. So you don’t have any concerns about it affecting the appearance of the seal. The temperature feedback to control system is based on the surface of the die, which is representative of the actual seal surface. Constant heat sealers are ideal for creating a peelable seal on laminated materials. Because the machines heat up and remain at steady temperature, the wear and tear is lower than that of impulse heat sealers. So, the maintenance required on a constant heat sealer is the lowest for any of the technologies we’re going to discuss today. They are also the easiest to validate and calibrate because again of their high level of repeatability and inherently stable state.
So interestingly, pouch manufacturers use constant heat sealer almost exclusively to form the pouch. This means that when you use a constant heat sealer to create that final sterile barrier seal, odds are that you’re using the same technology that is used to make the pouch. A common goal of a lot of medical device manufacturers is to make the appearance of the final seal match the appearance of the manufacturer seal. And in most cases, the most effective and efficient way of achieving that is usually by using the same technology, which is constant heat.
Also constant heat sealers don’t require a cool down time. So, the cycle rate for a constant heat sealer is higher than that of an impulse heat sealer but also lower than a rotary band sealer. And we’ll go into rotary band sealers next.
Guarding on a constant heat sealer must be appropriate to protect the operator from any burn hazards. So for this reason, the head space requirement for pouches processed on a constant heat sealer is larger than that of an impulse heat sealer. I’m not listing this in the challenges slide because much like the relatively lower throughput capabilities of an impulse heat sealer, this requirement doesn’t necessarily mean a negative, it’s just something to be aware of. You need more pouch room when you’re going to be using a constant heat sealer if what you’re used to is processing on an impulse heat sealer.
If you don’t have enough head space on your pouch to ensure your pouch can be pinched flat and fed naturally into the sealer beyond the guarding, there could be issues with the seal. So, if constant heat is your technology of choice, you need to ensure that you have the appropriate amount of head space to allow your materials to flow or line back together beyond the product, and then allow room for the materials to feed beyond the guarding and into the seal area.
Now, that amount of head space that’s required is determined by the individual manufacturer’s guarding and the model or configurations. So some constant heat sealers that have, for example, air evacuation gas flush because of the physical requirements for that have even more head space requirements than just a regular constant heat sealer that is not going to be processing modified atmosphere packaging.
So, while constant heat sealers do offer many positive attributes, there are some things that you should actually be aware of. The first is that it takes about 15 to 20 minutes for the sealer to warm up and stabilize at the set point temperature. Now, that can be shorter or longer depending on the temperature difference between your starting point and your set point. And the same is true when you’re changing over from one recipe to another, that requires a temperature change.
Constant heat sealers are also not really ideal for processing monolayer materials like the linear low-density polyethylene bags. Now, what I mean by that is if both sides of the pouch consists solely of LLDPE, and the goal is to create a weld seal, using a constant heat sealer is going to be challenging. If there’s any other material combined with the LLDPE, it’s usually not an issue. So, the LLDPE can be a part of a laminate, and that’s fine.
When we process monolayer LLDPE to create a weld seal, as I explained earlier, the monolayer material has to melt. And on a constant heat sealer, once you’ve reached that melt point, there’s no way to cool it down before you open the dies. In most instances, that means that the LLDPE weld seal made with a constant heat sealer is visually imperfect, to say the least, and with some lighter gauges of LLDPE, it can be really ugly looking.
So, high heat applications over 400 degrees are not appropriate on a constant heat sealer because the guarding… And this is a picture of a constant heat sealer without guarding so you can kind of see the physical dimensions of the system inside. So, heating up beyond 400 degrees would heat the guarding to the point that the guarding itself would become a hazard or the guarding would have to be designed so that it’s so far distant from the heat source that it won’t heat up, which is not really practical.
Because of the necessity for guarding and the larger die mass constant heat sealers usually have a larger footprint and consequently have a higher upfront cost than impulse heat sealers, but then they’re also typically smaller and less costly than rotary band sealers. So, that’s a good segue into rotary band sealers.
All right. So, we compared our temperature ways for impulse heat and constant heat sealers, which are categorized as bar sealers. And bar sealers have a defined cycle start and cycle end, but rotary band sealers don’t have a cycle per se, they’re continuously feeding pouches through the machine so our thought process of cycle needs to be modifiedal.
When the machine is started up, the heaters warm up while the bands run through the machine, getting everything up to set point temperature, and stabilized. To achieve this, there are two different types of heating systems typically used on band sealers. One is conductive heat and the other is convective heat. So, just to make sure we’re all on the same page, let’s just quickly define those.
Conduction is in short the transfer of heat through physical contact. The heater warms up the sealing die, and as the pouch is passed through the sealer, it comes into physical contact with the die, and the heat transfers from the die to the pouch. Convection is when liquid or air, and in this case we’re talking about air, is heated up and then travels away from the heat source, carrying the thermal energy along. And a space heater is a classic example of a convection heater. So as the space heater heats the surrounding air, the air will increase in temperature, expand, and rise to the top of the room. And this forces down the cooler air so that it becomes heated, and thus creates a natural convection current.
So in equipment, in band sealers, using convective heat isn’t… In band sealers that use convective heat, we don’t want to rely on natural convection. So, ambient air is vented into the sealer and directed over the cartridge heaters to superheat the air. A fan blows the air across several cartridge heaters, warming the pouch materials as they pass through the heater area. Both conduction and convection style band sealers use cartridge heaters. So we’re still using the thermocouple and the PID temperature control loop programming to control the temperature of the dies. For that reason, all the same pros and cons for constant heat also apply with some subtle differences, which we’ll get into.
Now, you may be wondering about that little graphic green leaf graphic. Searching for a graphic on the internet that compared conduction to convection was enlightening, because apparently there’s a lot discussion around the best method for processing marijuana. So, in the process of looking for a graphic, I inadvertently learned quite a bit. And that’s another discussion for another day. So, we’ll discuss pros and cons for both types of heat a little later, but first I want to just take a quick drive through the mechanics of the rotary band sealer and see what’s happening inside this machine.
So, I pulled this graphic off the web, and I’m not sure who sealer this is because it was from a third party part supplier website, but the graphic is extremely informative and I didn’t have to create my own, which is big bonus for me and probably for you too. So, to orient ourselves, the pouch is entering the sealer on the right side and exiting the sealer on the left side, in this image.
So, our pouch is going through the heater, and this is behaving very similarly to the constant heat sealer technology. The bands are running continuously. So the PID is already tuned for a constantly cooler material entering in from one end and heating rapidly as it traverses through the heater area. Putting a pouch into the system does provide an additional heat sink. So while more heat energy is pulled out from the heater, when a pouch is being processed, the relatively smaller heaters are able to respond quickly and replenish the heat rapidly.
So, the heaters in rotary band sealers are cartridge heaters, like that of constant heat sealers, but the die mass is smaller. So the heater is able to respond to the changes fairly quickly. By comparison I mentioned that constant heat sealers get to temperature in about 15 to 20 minutes, it’s typical for a rotary band sealer to get to temperature in about five minutes. So that kind of gives you an indication of the difference in the die mass that we’re talking about here.
Convection heaters are again cartridge heaters, but because they are not coming into direct contact with the pouch, the pouch does not act as a conductive heat sink. Hot air band sealers do require a slightly longer heating area because of the use of a more distant heat source and non-contact heat. So you’ll see in a couple of slides, there’s a picture of a heater on a convective band sealer or hot air band sealer. And the heater length is probably about double what you see here.
So, we have our sealing belt in this picture, which is used to process the pouch through the system. And you can just see it if you look at the roller area and can just make out the Teflon sealing belts that are barely visible in that area. In most cases, rotary band sealers also have a carrying belt, which transports the pouch through the system. But to avoid making this webinar on just rotary band sealers, we’re going to unfortunately jump over the belt discussion and continue with basics of the heating system. Maybe that’s a webinar for another day.
So, as you can see in this video that I’m about to load, one of the biggest pluses for rotary band sealers is regarding throughput. For a lot of medical device manufacturers who need to increase throughput, band sealers offer a good middle ground alternative between cycle-based bar sealers and high volume form/fill/seal machines. One great advantage is the fact that the operator does not have to hold the pouch, as you can see here, during the process time, or unload the pouch with every cycle. The operator puts the pouch into the sealer, and then the sealer takes it downstream from there automatically. Most users choose to run the pouch through the rotary band sealer vertically, which helps the product to drop into the bottom of the pouch and remain away from the sealer area. And in that video, they were running it as a vertical band sealer.
Some band sealers offer the flexibility to be oriented for running the pouches horizontally. So, I just have to say, just take a look at this guy. It’s an ocean nightmare, but what a great view of the mechanics of the system. You’ve got your sealing bands, the heater area, the homogenizing roller, cooling area, and then the drive area before we off load the pouch all within great view, but I personally would never want to run this machine. So, really because of the inherent heating and cooling process, band sealers are adaptable to seal pretty much any material successfully. Pouches of any width can physically be processed, because we’re not limited by a particular dialect.
In this photo, so just to orient ourselves, the heater block is the flat gold area to the right. So that’s where we’re going to look as we talk about this. The location of the heater area is the same regardless of whether you have conduction or convection systems. So, once the pouch exits our heater area, so it’s going from right to left, it passes between two wheels that push the pouch materials together, again for both types of sealers, but this is where it gets a little interesting and where they diverge a little.
With conduction systems, the heated dies are already making contact with the pouch and are physically pushing those pouch materials together. The seal is actually happening in the heater area, and the wheels at the heater exit end are used to just reinforce the pouch materials have made intimate contact in the heating zone, basically to homogenize the seal. For convection heaters, the roller area is critical in creating the seal. Without this zone, the pouch has not experienced any pressure, and the pouch materials have not been forced together. So, the air is blown on the pouch material as it passes through the heater area.
And here we can see, I’d mentioned before, that the heating zone is double the length of a conduction heat system, and that’s indicated by those red stickers in front of each pair of heaters. But note that no force is being applied to the materials in this area. Once a pouch exits the heater area, a pair of wheels press the material together to apply pressure and force those two pouch webs together.
Once the pouch moves past the roller area, it enters into a cooling area. And this is necessary because the pouch is moving pretty quickly through the system. And if we were to simply allow the pouch to exit the sealer at this point while it’s still warm, the seal would still be setting and would probably create wrinkles, or have issues with our seal. The rest of the stuff on the left here is the drive section, which is interesting, but a little off topic from our discussion of the temperature process on rotary band sealers.
As we mentioned, rotary band sealers provide faster throughput than bar sealers, and that’s wonderful, but all those moving parts do translate to more maintenance. So don’t just assume that more is better. Select a sealer that best matches your needs, and then that way you’ll get the best possible solution for your application. Band sealers have a larger footprint and a higher cost than impulse or constant heat sealers. And the use of a conveyor may be helpful to support the pouch and the product as it’s supported through the system. And a conveyor is necessary if you’re running the pouches horizontally through the sealer.
So, we’ve seen how band sealers really win when it comes to throughput and flexibility. But as we said in the beginning, no technology is 100% perfect. So let’s take a look at the challenges. The bands are moving at a pretty good clip, usually around 350 inches per minute. That movement can generate particulate from the Teflon bands, especially if pouches are not actively being processed and the machine is on standby and still running, but not actually processing pouches.
If the sealer has sealing bands separate from the transport bands, so you could have the sealing bands and then the carrying bands or transport bands, the motors for those two different bands need to be perfectly synced, or you can get visual imperfections in the seal area known as a zebra effect, which look pretty much like it sounds with lighter lines separated by darker lines. And the result of that is the pouch is actually skipping due to the motor speed differences between those two motors.
Because the pouch is being pulled through the system, there is the chance for larger pouches with dissimilar materials, so like Tyvek on one side and film on the other, for example, to have wrinkles in the seal towards the trailing edge of the pouch. And this concern is not as prevalent for narrower pouches or pouches with the same material on both sides, because they heat up and expand at the same rate, or there’s not as much material to get out of alignment with each other.
So there are some additional challenges for hot air systems over and above rotary band sealers in general. Let’s just quickly touch on that. So, the use of hot air increases air movement in the clean room, specifically around the seal area. Since we already know that wear and tear on the Teflon bands can create particulate, the air movement can disturb that particulate and cause it to become airborne. Not a great situation in the clean room.
Also, hot air is also very susceptible to environmental influences, so you need to be aware of air flow if you’re using a hot air band sealer. Almost done. Okay. So, we’re doing on time pretty good. Now onto form/fill/seal machines. So, there are two primary types of pouch form/fill/seal sealers, vertical and horizontal, with vertical being by far the more common.
While used primarily in food applications and not widely used in the medical device or sterile packaging applications, pouch form/fill/seal absolutely have their place. I’ll just say, as a result of the limited use of form/fill/seal pouch sealers in sterile packaging applications, I don’t have a lot of photos. So I’ve interspersed some of these with food packaging applications, just to kind of illustrate the idea and get that across. So, please just bear with me on this.
Unlike bar sealers or band sealers, form/fill/seal machines don’t require the use of preformed pouches. Instead, two rolls of materials are fed into the sealer, forming the pouch in line. The product is loaded either manually or automatically, and the sterile barrier seal is created in one shot, hence the name form/fill/seal.
So, what’s going on inside a form/fill/seal machine? It’s a close cousin to a bar sealer in that it uses constant heat and is cycle-based, but unlike bar sealers, the flexibility for form/fill/seal systems is two-fold. That’s hard to say. We can process horizontally or vertically, and there are two different ways in which the machine can create the pouch in line. And to get a better understanding of that, I have a video of one in action.
So, this is a video of a large machine doing a bulk seal application. So like I said, just bear with me, because I have to reference some other types of industries here. And as I go through this, I’m going to refer to pouch one and pouch two to explain what’s going on. So the material is indexed automatically down into the machine, and the dies close to create the bottom seal for pouch one. So there we’ve got pouch one. The product is filled into the pouch from above and then the material is further indexed down. The top seal is applied to pouch one, and at the same time, the bottom seal is applied to pouch two.
Simultaneously, finished pouch one is trimmed from the rest of the material above, so on and so forth. So it keeps on going automatically. Once again, we’re using constant heat and conductive heat in the process for all form/fill/seal machines.
So, as we can see in this video, the type of material being processed here or the type of pouch that’s being formed is a gusseted too, but the pouch can alternatively be formed on all four sides in line. So just like we saw in the application for the bag of seed, the same process is employed, but now instead of a simple bar at the bottom that’s forming that bottom seal and also the top seal as it indexes through, we have a frame. It’s hard to see in this picture, I know, but you can kind of just see beyond those two bolts, there’s a kind of a pouch there. And then around that is the frame for the making the actual seal. And that frame is forming the bottom and the size, and then it indexes to form the top and trims.
As the material is indexed automatically into the sealer, the product is dropped into the pouch either manually as you see here or automatically. Because of the speed required for form/fill/seal applications, this type of sealer does not lend itself to impulse type technologies or hot air heating.
One of the biggest reasons someone would choose a form/fill/seal is because of volume. It has the highest throughput of any of the machines which you might think could be challenged by rotary band sealers. But when you also take into consideration the pouch prep required for rotary band sealers, when you saw how fast that guy was pushing it through, but all of those had already been prepped. Form/fill/seal machines are just much faster when you take that prep into consideration.
So, with form/fill/seals, the only operation the operator’s doing is dropping the product into the vertically oriented pouch or laying it onto a horizontally oriented bottom web. I mean, this is not a great example, but it gives you the idea kind of like you see here. There’s no requirement like there is with rotary band sealers to pick a pre-formed pouch, open it, insert the product into the pouch, and so on and so forth. When you look at it this way, form/fill/seal machines can save a significant amount of time and provide unparalleled throughput.
You can also save money on pouch material since you are purchasing rolls of material and handling the pouch forming process yourself. Purchasing pre-formed pouches is consistently a higher cost than buying rolls of material and making the pouches during the product packaging process.
Most form/fill/seal machines are dedicated sealers. To justify the substantially higher cost of a form/fill/seal machine, the individual product volumes should be calculated to necessitate this technology. I’m not saying it has to be a dedicated sealer, but to really make the most of the value of a form/fill/seal machine is probably going to be limited to running just one or a few products that are changed out infrequently.
One consideration for bar style form/fill/seal machines is that both ends of the seal pouch have to be a square seal. Because you’re using the same bar to make both the top and the bottom seal of the pouch, or if you think of it in the process, the bottom and the top seal of the pouch, you can’t make a chevron pouch. You can make a chevron pouch if specific pouch tooling is used to form the pouch on all sides.
There are, as we saw, a few different versions of form/fill/seal machines, and I realized this is a horizontal tray form/fill/seal, not pouch, but it’s hard to find a photo of a horizontal pouch form/fill/seal. So, bearing with me again. Determining a vertical, which utilizes the smallest footprint, or horizontal which you see here, which enables you to use longer pouches is the right fit for your application can be very project-specific.
Vertical form/fill/seal machines, especially those employing a manual product load, need to maintain an ergonomic height for the load area. If longer pouches are required, then it might be best to look at a horizontal form/fill/seal. Form/fill/seal machines have the highest upfront cost, and by far have the largest individual machine footprint. But if you take a look at a footprint of one vertical form/fill/seal machine compared to the footprint of a quantity of bar sealers capable of producing the same throughput, and this is not to size, by the way, the form/fill/seal machine can probably take up less space overall, and definitely requires fewer operators.
So, I had mentioned before, you didn’t want to see my graphics, this is the type of graphic that I make. Yes, I made this, it’s pretty basic, but I kind of felt like Bob Ross with my happy little people, made me feel happy too. Anyway, so unless you’re using two type roll stock, which most sterile packaging applications don’t, a considerable challenge for form/fill/seal machines is the tooling required because they are making the pouches to size.
The lot size for most medical device packaging applications does not necessitate a dedicated form/fill/seal machine. So, downtime for tooling changeover as well as the cost for individual tools becomes something of a consideration. Obviously due to high processing speed employed by form/fill/seal machines, maintenance becomes a frequent necessity, and unscheduled downtime can have a huge impact.
Lastly, one significant challenge for sterile packaging applications is validation. Validation becomes a little trickier for a number of reasons. First, you’re forming the entire pouch not just the final sterile barrier seal. So ensuring that the entire usable seal area meets the accuracy and repeatability specifications on all four heated dies needs to be taken into account. Additionally, you absolutely need to take into consideration the hot tack property of the materials. And this is probably one of the biggest considerations for vertical form/fill/seals.
The time it takes for the bottom seal to set before allowing product to be dropped into the pouch and potentially interfere with the appearance of that seal while it’s still setting is critical to the process, especially if the product is heavier or bulkier, and may put additional stress on the bottom seal during curing time.
So, as we noted way back in the beginning, it seems like that was such a long time ago, at least for me, time or speed is another critical element to creating the sterile barrier seal. So, we’re past the heat, now we’re onto time, and then we’ll go onto pressure. So, time has to be absolutely consistent and repeatable. Likewise for rotary band sealers, speed has to be consistent. All the equipment must be capable of being validated to demonstrate the repeatability of the system.
For cycle-based sealers like bar sealers, proximity switches can handle the start of the timer, and then the program determines when the cycle should end. The proximity switch on the bar can also be used to not only start the dwell time, but can also be programmed to confirm that the bar has indeed physically closed, and then opened as anticipated. This mechanical confirmation can also be used for form/fill/seal machines.
For rotary band sealers, a timing belt connected to an encoder accomplishes the same level of repeatability to ensure the pouches are being processed at a consistent speed and are being… Excuse me, exposed repeatedly to the heat every time a pouch is loaded into the machine. I have a squeaky chair. Sorry, if you can hear that.
So, pressure or force is a little more complex. Let’s see if we can wrap this up quickly, we’ve got seven more minutes left, because we’re one slide away from Q&A. So, I had mentioned in one of the earlier slides for impulse sealers that Cantilever Presses should be avoided. And this is a big concern for ensuring you’re getting equally distributed force across the entire usable seal area.
Direct motion cylinder presses are best, but any press that moves the entire bar in a uniform motion on the same linear plane will give you the best opportunity to apply the same amount of force for the same amount of time across the entire pouch, whether it’s a bar sealer or a form/fill/seal machine. Alternatively, because on band sealers the pouch engages the heater at the in feet end or the extreme end of the length of the heater, band sealers should as a best practice use a floating press design so the press can pivot. As the thickness of the pouch enters into the heater, flattens out as the pouch takes up the entirety of the heater area, and then pivot back down as the pouch leaves the heater area. As the pouch enters into the roller area, the rollers, which are compliant, help to press the two sides of the pouch together.
If the system is pneumatic, either internal or external accumulators will help prevent pressure drops upon cycle initiation. And this is super important because other equipment could be cycling at the same time, drawing from the same compressed air source, and starving that line of air. So the time it takes for the press to close could vary from cycle to cycle, if a protected air reservoir or air accumulator like you see in this photo is not provided for each machine.
If a press closes slower on one cycle than another, the proximity switch placement could be really, really critical. So, if it’s closing more slowly on one cycle, depending on where that proximity switch is mounted to the sealing die, the dwell timer could start before the press has fully closed or achieved minimal pressure translating to a shorter cycle and ultimately a non-compliant pouch.
So, that concludes the pouch sealer technology comparison. Looks like we have a couple of minutes for some questions. So, I’m going to shoot over to my Q&A here. Sealing belt rubs on the cooling block, correct. Pouch pinched between upper and lower belt. So, yeah, absolutely. We got a question. The sealing belt as it’s going through the rotary band sealer will rub on the heater and the cooling blocks. It definitely rubs on the heater block. And that’s what can generate some of that particulate. So, yes, if that Teflon cloth is running through the pouch, you’ve got your band sealer running, and if it’s dry cycling, which means you’re not actively running pouches through, then that particulate kind of just gathers on those Teflon cloths. And especially if you’re doing hot air and you’re blowing air, then that gets airborne and can potentially get into the pouch during the sealing process.
So, we have another question here. What is the best type of sealer for gusseted bags? So we had looked at that gusseted bag that was the seed application. That’s a really great question. So, best type of sealer for gusseted bags, I mean, you could use a constant heat sealer or an impulse heat sealer, but that’s going to be really, really critical in making sure that you have heat on both sides. Because with gusseted bags, you’re going from two layers in the middle to four layers on the ends, and you want to make sure you’re getting enough heat through both sides of the pouch to be able to seal it effectively and efficiently without having to have the heat migrate through the entire pouch from top to bottom from one direction.
But as I had mentioned about band sealers, because of the ability for the floating heater to pivot, band sealers can be one of the best technologies to use for gusseted bags because they can accommodate those differences in the thickness of the pouch when it goes to those four layers to the single layer.
We have I think time for one more question. Can a rotary band sealer be used in an application that requires vacuum? So, I will say yes, it could absolutely be used in an application that requires vacuum, but under certain conditions. And it gets a little tricky, because you are constantly processing pouches through, and like I said, averaging about 350 inches per minute, so you’re moving at a pretty good clip, the opportunity for a nozzle to enter the pouch, evacuate out the air from the pouch, if you’re going to do a back flush of an inert gas like nitrogen or argon, you have a very, very small window of opportunity for getting that nozzle into the pouch and processing the modified atmosphere for that pouch before it needs to get out of the way of getting into the heater area.
So, it absolutely can be done, it just… you need to take into considerations, size of the pouch, how much do you need to modify the atmosphere inside that pouch? What throughput do you need? And you may need to slow down your speed on a band sealer if you need to modify the atmosphere more than what you can do in the short window. There are other types of solutions for modifying the atmosphere to a greater depth, but those are usually offline and you take the modified pouch to the sealer, so that can affect throughput too.
I hope all of this information was valuable to everybody, and I hope you enjoyed it. And we are at one o’clock on the dot. So, I appreciate you dropping in, and I look forward to the next webinar. Thanks so much.
