Technology continues to amaze me. I’m sure I am blind to a majority of what is out there outside the packaging world, but from what I am aware of, it makes me wonder how I ever lived and managed to miraculously survive in a world without even the now commonplace cell phone. I just watched a video last week of a house that was made with a 3D printer. In one day! I’m impressed.
How have we seen these advances translate into the packaging industry? Even though ultrasonic sealing with plastics has been around since the 60’s, about ten years ago, we started to see ultrasonic sealing trending in the Packaging Industry. This innovative technique to sealing was (and is) exciting, because of the implications it proposed as far as extending capabilities in certain areas. This technology uses acoustic vibrations which allows the material to seal without the need for direct heat on the material. Also, it is capable of sealing through product. That in itself can be an advantage for applications and we see this often with the packaging of fresh produce.
Since the absolute best packaging solution for each application is (or should be) everyone’s goal in the packaging industry, let’s explore how ultrasonic sealing compares with the traditional heat sealing method and evaluate if it is necessary for your stand up pouches or pillow bags. After all, as cool as it is, just because a 3D printer can create a livable house, it does not mean that the house is a fit for the needs or wants of you and your family.
Because the seal is typically considered to be much smaller with ultrasonic sealing then with heat sealing, estimated at up to 75%, it is perceived that ultrasonic sealing excels in this category. While it may have a smaller seal, the difference between seal length is not necessarily as small as one might think. In a recent comparison Rovema conducted with one of their clients, they were able to decrease the difference in seal width to 2 mm. With the knife gap included in both sealing methods, ultrasonic sealing length ended up being 4 mm while Rovema’s engineered solution was a 6mm seal. In this case, the customer decided to go with the heat seal option as the 2 mm difference was not as important as achieving a higher BPM (bags per minute) rate.
We see that with the larger seal that is typical of heat sealing, you have a benefit of a more secure seal due to the width. On the other hand, the smaller seal created by ultrasonic sealing can provide less waste of raw material.
Another aspect of seal width is appeal. A recent article in Packaging News pointed out that some customers, especially in the snack industry, prefer the look of a thicker seal. Aesthetics is ultimately perspective, however, and the image that works for one brand may be irrelevant for another.
Bags Per Minute
Conduction sealing is the current winner in the BPM competition. This rate can change depending on product, film, machine, and other factors. All things being equal, heat seal technology surpasses ultrasonic in BPM and often sees increases of 40 + bpm over ultrasonic sealing. While ultrasonic technology has and is continuously making improvements, heat seal is still able to match and exceed bpm rates. The consideration here is how many bags per minute do you need or want from your machine.
What is your experience with BPM in ultrasonic sealing vs. heatseal?
Ultrasonic sealing takes the lead when it comes to lower energy consumption. In a study conducted by Bach, Thurling, and Majschak they determined that:
“Interesting is the fact that the energy consumption for ultrasonic sealing is almost independent of the machine speed. In ultrasonic sealing, energy is consumed only during the sealing process itself, except for some joules for continuous operation of the generator. In conduction sealing, the bars have to be heated all the time. They permanently emit energy via convection and radiation, even when nothing is being sealed or the machine stops. The energy consumption for conduction sealing strongly depends on the machine speed and is reduced at increased machine output”
So, the higher the output, the more favorable the energy consumption comparison. The lower the output, the more negative. Film type can also affect the variances in consumption. Regardless of film type or output, energy consumption is one area where ultrasonic technology excels.
Upfront, heat sealing technology is a much cheaper alternative. When looking at the total life cycle, ultrasonic sealing appears to begin to make up for that with its lower energy consumption and raw material waste. Unfortunately, as you factor in the expensive replacement parts of ultrasonic sealing we begin to once again see the price advantage veering toward the heat seal.
Another advantage often touted for ultrasonic sealing is that it is beneficial for products that are more sensitive to heat such as chocolate, cheese, produce, and other items. This particular point is actually not as relevant as it appears at first glance. Many VFFS machines can incorporate bevel plates in their design specifically for these sensitive products thus preventing the heat from interfering with the structural stability. The real benefit of ultrasonic sealing has more to do with its ability to seal through product, which is a reason why we see this being used more frequently with salad and fresh produce.
Some VFFS machines which are set up for ultrasonic sealing are capable of exchanging sealing methods. Switching out the jaw, you could go from a heat seal to an ultrasonic seal or vice versa. I cannot speak for all manufacturers, but this process is able to be completed in under 10 minutes with Rovema's BVI or BVC machine
The type of sealing technology to use can be dependent on what you need for your product. We all want to be front runners in innovation and trends. But more than anything, we want to make sure the right solution goes to the right application.