It's sophisticated, clean and cool, but is ultrasonic sealing really a serious challenger to the ubiquitous heat seal? Lynda Searby takes a look at some of the technological developments in the sector to find out

Heat sealing has long reigned supreme as the technique of choice for sealing flexible bags and pouches made on form, fill and seal (FFS) machines. However, ultrasonic technology is increasingly challenging and, in some cases even usurping, heat sealing in certain applications.

Ultrasonic technology uses acoustics (mechanical sound waves) to create a molecular bond between plastic materials. "Ultrasonic sealing is a method for joining thermoplastic materials together by emitting acoustic vibrations," explains Andreas Graf, product manager at Sigpack Systems, a part of Bosch Packaging Technology. "The film is sealed with heat from friction generated by an oscillating tool, eliminating the need for direct heat contact."

Removal of the heating element has several benefits, according to Graf. It enables ‘cold' packaging of sensitive products, such as delicate confectionery, grated cheese, fresh produce and frozen food. It also means less energy is used, making ultrasonic sealing ‘greener' than heat sealing.

"The energy and heat necessary for ultrasonic sealing are generated from the inside and emanate outwards," he explains. "The result is a marked improvement in energy efficiency. In fact, ultrasonic sealing reduces energy consumption by around 30% when compared to heat sealing."

In addition, he says the use of cold sealing jaws makes the packaging machine more efficient. "The agglutination of hot sealing jaws with foil leftovers results in maintenance and machine downtime. The cold sealing jaws used in ultrasonic sealing negate the problem of foil leftovers, reducing delays on the production line."

Another advantage of ultrasonic versus heat sealing is the film that can be saved, as the seals at the longitudinal and transverse seams are narrower, so less packaging material is required. "On salad bags, most heat seals are about 30mm or 32mm deep, whereas you're looking at just 8mm with an ultrasonic sealing system," says Chris Creasy, industry manager for the salad industry at Ilapak. "So you're looking at a cut-off length of about 230mm with a conventional system. Straight away you can shave 24mm off that with an ultrasonic system, which equates to a 10% saving on film."

While these benefits all contribute to the case for ultrasonic sealing, at present, the overriding reason packagers and processors are moving to ultrasonic is because of the seal integrity it offers. "The main advantage of ultrasonic sealing is the level of seal integrity that can be achieved," says Tim Dowling, project engineer with Selo UK. "Ultrasonic sealing can seal through most product residues, that could have accidentally been deposited in the seal area."

Examples of products that are prone to contaminating the seal include salad leaves, grated cheese, powdered mixes and liquids, which may splash and spill. Ilapak has supplied several of its Vegatronic 2000 and 4000 VFFS systems fitted with ultrasonic technology for salad leaf applications.

New installations
Selo has been focusing on incorporating ultrasonic sealing into the Toyo Jidoki rotary pouch filling and sealing machines it supplies to the food industry. Five systems are in operation across Europe. These are being used for packaging baby food, soup and ready meals.

The company is also looking into ultrasonic sealing on multi-lane stick pack machines for pharmaceutical liquids and VFFS bagging for dusty powders and dairy applications. In addition, Dowling says ultrasonic sealing will be on stream for both centre and end-seal units for HFFS flow-wrapping machines within months.

Spanish company Volpak, represented in the UK by Integrapak, has supplied horizontal FFS pouch makers for cake mixes and liquid products. On the Volpak systems, ultrasonic sealing is only used on the top seal of the pouch, as this is the main area of concern and the side seals are created before coming into contact with the product.

Bosch, meanwhile, can deliver ultrasonic sealing on horizontal flow-wrap machines for packaging ‘solid products' in pillow packs, as well as on its VFFS SVE2515WR machine for producing stand-up pouches, gusseted and pillow bag packaging formats for confectionery, cheese, fresh produce and frozen food.

While ultrasonic sealing is now available on both vertical and horizontal FFS machines, the technology is still very much in its infancy for horizontal flow-wrapper applications. "For vertical applications this technology is about two years old. When it comes to horizontal it is very new and just a few companies are dealing with it at the moment," says Graf.

With ultrasonic promising so many advantages, you might well wonder why anyone would still use conventional heat sealing, but the technology does have limitations. For one, Bosch admits that speeds are not as high as with heat sealing, though it does expect to see improvements in this area over the next few years.

Another problem with ultrasonic - which may not be so quick to overcome - is that the technology is limited to certain film types and thicknesses. It is for this reason that Ishida Europe, which supplies VFFS machines to the snacks industry, is steering clear of ultrasonics. "It's not really suited to the types of films used in the snacks industry," says Kevin Ferris, product manager for the company's bagmakers. "To create an ultrasonic seal you need a reasonably thick sealing layer on the inside of the film. For snacks, OPP is normally used, and that has a very thin sealing layer."

Ultrasonic seals differ in appearance to heat seals, too, which could put some users off. Selo UK says to counter this it only replaces the primary sealer of the two-stage sealing system on its pouch fillers. This means the system delivers the high integrity narrow ultrasonic seal and then over-seals with a 12.5mm heat seal which has a smoother and cleaner appearance.

Initial outlay
This might solve the aesthetic problem, but if you have to use ultrasonic sealing in tandem with heat sealing, it could start to become a rather expensive option - particularly as ultrasonic-sealing machines cost more than heat-sealing machines in the first place.

In fact, even proponents of ultrasonic technology admit it is considerably more expensive than heat sealing. Ilapak estimates that, on average, a VFFS unit with ultrasonic sealing will cost £45,000 more than a unit with heat sealing. While this might still sound like a large premium to pay, Creasy says that for companies who have a problem with seal contamination, the payback period can be as little as 12 months, making it an economically viable proposition.

"If you consider that every time you get product stuck in the seal, you waste two bags and have to rework the product, you begin to see what a significant difference high-integrity sealing can make. A company with a remake rate of, say, 7%, will see a fairly quick return on investment," he says.

Bosch's Andreas Graf also argues that the higher capital outlay can be justified by the cost-saving benefits of ultrasonic sealing. "At the moment, ultrasonic sealing is more expensive than heat sealing because it is a new technology, but there is a quick return on investment as the smaller sealing seams result in less material wastage."

For those companies who are not convinced by the ultrasonic arguments, there is a third way. Omori, a Japanese company represented in the UK by Selo UK, launched a flow wrapper with an infrared sealing system at last year's Japan Pack.

According to Selo's Dowling, this reduces power consumption by 22% and heater warm-up times from around 15-20 minutes to 3-4 minutes compared with a typical heat sealer - and it doesn't cost any more than its heat-sealing counterparts.

Looking to the next few years, it is unlikely that ultrasonic will overtake heat as the sealing technique of choice, owing to its limitations and the fact the cost difference can't be justified in some applications. However, in applications where seal integrity is paramount, such as pharmaceuticals, infant nutrition and high-risk foodstuffs, and where seal contamination is a costly problem, it's fast becoming a no-brainer.

FORM, FILL AND SEAL ROUND-UP
• FFS machines from two Spanish companies are now available in the UK from Integrapak. Inever manufactures multi-lane stick pack machines with an integrated laser for creating easy-open tears, while Synchropack manufactures horizontal flow wrappers.

• PFM Packaging Machinery launched a new reclosure system for flexible packaging at this year's PPMA. The system, which is said to combine the strength and life of a zipper profile with the ease of use of adhesive-based systems, was demonstrated on PFM's BG4800 EWL MAP flow wrapper.

• Riggs Autopack used PPMA to promote its new semi-automatic stand-up pouch filling and sealing machine. The rotary machine is aimed at small to medium-sized companies making liquid foods, such as soups and sauces.

• Launched in September, the new HTS (horizontal top seal) flow wrapper from Redpack Packaging Machinery is said to combine rugged construction, a stainless-steel finish and a small footprint, making it suitable for the food and fresh produce industries.

• Summer 2009 saw the introduction of Kliklok-Woodman's new VFFS twin-tube bagmaker, the G3. The G3's welded tubular steel frame is said to have been designed to fit a smaller footprint than most twin-tube bagmakers and allow weighers and volumetric fillers to be direct-mounted to the machine.

• Known as the ‘twin configuration', the new TNA Robag 3 ttx 320 Rotary Double Jaw combines two VFFS machines in one footprint, doubling production rates.