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Sealing the weakest link | Buyers’ Guide – Capping, lidding and sealing

March 4, 2013 1 Comment » Print Print

The seal is the weakest link in any heat sealed pack, but can anything be done about it? Lynda Searby finds out more and rounds up the latest kit coming onto the market

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When I opened the fridge to make brunch one recent Saturday morning I was dismayed to find that the bacon I had bought the week before – although still well within its use-by date – was definitely not fit for consumption. Missing out on a bacon butty was not enough to send me running back to the supermarket, so the faulty pack went unreported. But it does prompt questions over leaky seals – how big a problem is it in the food industry?

Most evidence on leaky packs is anecdotal, although a 2009 report titled ‘Seal integrity and the impact on food waste’, produced by the Waste and Resources Action Programme (Wrap) and researchers at the University of Lincoln, does provide some concrete data.

From audits carried out on 105 heat sealing units (including vertical and horizontal form, fill, seal machines, tray and pot sealers and flow wrappers) across 11 factories in the UK, the researchers found that 24% of packs exhibited seal problems. However, only 1% of packs were identified by factory tests as being sufficiently damaged to be rejected by factory quality testing systems. This means that a far greater proportion of packs than are currently being detected through quality control might well fail to provide sufficient protection to the food through the supply chain and into the home.

While the consumer might feel a bit disgruntled, the biggest impact of leaky seals is felt by the food manufacturer, according to Gary Tufnell, product development manager, tray sealer and line solutions at Ishida Europe:  “Retailers will send entire batches back, resulting in fines and loss of revenue for the producer.”

The Wrap study found that the most common reason for seal failure was product contamination in the seal area and that sealing problems were more common where products had liquid and crumb components.
This finding seems to be supported by those involved in the supply of heat sealing equipment. Packaging Automation commercial director Sam Ashton says: “Contamination can be a major issue when the product contains sauce, oil or grease and is hand loaded into trays. For example, a protein with sauce may be hand placed or scooped into the tray, which allows grease or sauce to smear onto the tray flange. This interferes with the bond between the sealant layer on the film and the tray and can cause weak seals that may deteriorate over time.”

Tony Burgess, head of sales and control systems with Proseal, notes that contamination of the seal area can also be a problem with meat and ready-to-eat fruit salads, as juices and membranes can interfere with the seal.
“We deal with that by modifying the seal profile we employ or through our hot rod technology,” he says.

Proseal’s hot rod heating system focuses heat on the tray contact face, improving heat replenishment and preventing heat from being drawn out of the tool. “Hot rod technology is particularly useful when sealing onto smooth-walled foil trays, which can be very cold when they enter the machine,” adds Burgess.

Increasing seal force

Proseal also offers a patented seal force system which is said to increase seal force by as much as 190% over conventional sealing machines. The EcoSeal system ensures that seals are of the highest standard and reliability, says Proseal.

Ishida’s Tufnell, meanwhile, cites loose leaf salads as the most challenging product to seal, as stray leaves can get caught in the seal. To overcome this problem, Ishida has developed filling systems that tuck overhanging leaves into the tray.

The heat sealing unit itself may also be responsible for creating faulty seals if it is poorly maintained or set up incorrectly.

“Poor maintenance of heat sealing tools can be another common cause of incomplete seals,” says Ashton. “For example, worn or damaged rubber will not support the tray flange adequately when pressure is applied, leading to weak spots. Missing springs again prevent adequate compression.

“In addition, if the machine is operated outside the pre-set standard temperature and seal time for the particular tray and film, the optimum bond will not be achieved,” she says.
Packaging Automation’s Eclipse machines store the settings in the HMI screen under specific recipes for each product that is packed and these do not need to be altered if the correct recipe is selected at the start of the run. Temperature and seal time settings can be password protected to prevent operators from changing them.

When it comes to set-up of heat sealing machines, John Rose, director of Raque Food Systems, explains that there are three variables that create a seal: time, temperature and pressure.

“All three elements have to be set correctly for efficient sealing and with a good quality machine, some of the container contamination issues can be tolerated and still give a good seal,” he says.

However, he warns that if any one of the three elements is not set correctly, the seals will be of a poor quality. He claims Raque’s machines are designed with the ability to generate as much sealing time as required, deliver very sensitive temperature monitoring of each sealing head and produce greater sealing forces than rival equipment.

Ishida’s Tufnell has witnessed instances of operators setting the sealing temperature so high that the heat seal tool delaminates the packaging film. “We can put a maximum tolerance on our machines so that operators can’t change machines to go outside the acceptable range,” he says.

Tufnell says another major cause of seal failure is incompatible materials. “We sometimes get customers changing their film specification or switching to a cheaper alternative, which results in incompatibility issues,” he notes.

According to Packaging Automation, this has become a more common issue as food producers come under increasing pressure to cut costs, and Ashton explains why it can lead to seal problems. “Each heat sealing tool is designed to a particular tray’s dimensions. Any changes to the tray, for example to a thinner gauge tray, could lead to a small but important change to the tray dimensions. Issues have been seen where the tray will not sit correctly in the base tool and distorts when sealed, leading to an irregular bond.”

While some of these issues have been addressed through design features on heat sealing equipment, the other part of the solution lies in quality control systems for checking seal integrity before packs leave the factory.
Lynneric Potter of Campden BRI’s packaging team explains: “There are a number of test methods manufacturers can use to carry out integrity tests. However, most of them are off-line and destructive methods whereas what the industry wants and needs is a 100% on-line inspection system which will check all seals and not compromise their production rate. It is also important to select the correct equipment for integrity testing because some equipment can only detect a certain size of leak.”

Gas analysis

On-line equipment does exist for gas analysis. Both Kern and Ishida, for example, offer on-line gas analysis equipment for use with modified atmosphere packs to make sure every pack contains the right combination of gases.

Jenton Ariana, meanwhile, offers an on-line system for gas flushed thermoformed packs. The Autotester features test heads that simultaneously pressurise and leak test gas packs and either accept or reject packs on grounds of ‘overgas’, ‘undergas’ or ‘leak’ using very sensitive transducers. The system can test up to 180 packs per minute, will not slow the thermoformer down at 15 cycles per minute and detects pin holes of 0.3mm or more, claims Jenton.

For the vast majority of heat sealing lines though, no commercially viable on-line seal inspection system exists. Until this situation changes, bacon butty lovers everywhere will continue to be disappointed.

Product round-up

Crown launched a capping machine last autumn for small and medium sized manufacturers and bottlers. The Smart Capper, which is designed for capping glass jars and bottles, is said to provide quick and easy manual cap and glass size changeovers. The machine can run at up to 150 caps per minute, and can be operated at a speed adapted (via an electronic link) to the rest of the production line, for heightened efficiency.

Last year’s Anuga FoodTec was the first outing for Sidel’s new high speed aseptic filling and capping machine for teas, juices, nectars and isotonics. The new high speed version of the company’s aseptic Combi Predis FMa is capable of handling up to 48,000 bottles per hour for small containers of up to 700ml. The applications are used mainly for on-the-go consumption.

Dico & Gravfil has unveiled a new generation of liquid filling and capping equipment for use in the petrochemical, agro-chemical, household product and food industries. The Dico-Delta capper can achieve speeds of up to 400cpm and the Gravfil-Excel liquid filler is capable of filling container volumes from 50ml to 5l. The lines use energy-saving Siemens hardware to reduce operational costs and advanced remote diagnostic capabilities for maximising machine uptime.

Star Product – RDM Seal-Scope and Seal-Cam

The commercialisation of a seal inspection technology, developed by researchers at The University of Leuven, means that it is now possible to test seal integrity at the point of production without compromising line speeds.

The technology was introduced by Engilico last year under the Seal-Scope and Seal-Cam brands in Belgium and Holland, where between six and eight systems have already been installed. Now Hertfordshire-based RDM Test Equipment has been appointed to distribute the systems in the UK and Ireland.

The Seal-Scope and Seal-Cam units generate a unique ‘seal fingerprint’ for every package, which is compared to statistical data to determine pass or fail.

The technology is based around a highly advanced statistical algorithm that also monitors trends in seal process capability, enabling early warnings when pre-set limits are reached. The system is capable of detecting incomplete seals, wrinkles, folds, creases, holes and product or contaminants in the seal.

“It does all this within a few milliseconds – takes the signal, processes it and ejects imperfect packs, so factories won’t have to slow down their production,” explains Phil Neal, director at RDM. “Currently, companies commonly perform manual squeeze tests or use basic leak testers. This comes at the problem from a different angle in that it looks at how the seal is formed.”

Seal-Scope analyses the vibration burst signal from a sensor on the sealing bar, and is suited to most vertical and horizontal form fill seal machines. Seal-Cam, on the other hand, captures an infra-red snapshot of the residual heat at the seal, which makes it more suited to checking yogurt pots, blisters and trays. As Seal-Scope and Seal-Cam only launched in the UK in December, there haven’t yet been any installations, but Neal says the first machines are expected to go into food factories in the next few months. The systems can be retrofitted into most existing packaging lines.

Star Product – Ishida QX-775 Flex Tray Sealer

The QX-775 Flex is an upgraded version of Ishida’s QX-775 tray sealer, and is said to combine speeds for modified atmosphere packaging (MAP) trays of up to 15 cycles per minute with an open, hygienic design and high quality pack and product presentation.

The new upgraded model is suitable for any product type including ready meals, meat, poultry, fish and salads. It is also compatible with a variety of packaging applications including standard MAP, skinpack and shrink film applications. The machine’s servo-driven motion is the key to higher throughput, as this enables accurate tray handling at high speeds.

Product quality features include the ability to disable a sealing head in the event of a sealing head error, a ‘smart’ belt system that alerts operators to out-of-spec packs or misplaced products or trays, and an in-built gas analyser that samples the gas at every cycle and automatically stops the system if the wrong mix is detected.

The tray sealer’s control system includes auto-set features for integrated film coding, gas mixing and analysing, allowing one button product changeovers. The servo-controlled film drive ensures smooth handling of the film and accurate printing for integrated coding systems, says Ishida.

The machine has been designed so operators can change films and tools using automatic and quick release features – particularly useful for ready meal applications where product range and production volumes can fluctuate.

Self-draining curved surfaces, the absence of exposed cables or motors and easy-to-remove belts and conveyors have all been incorporated into the tray sealer’s design to allow a fast and comprehensive wash-down.

Case study- Proseal GT2 Tray Sealer

Scottish soft fruit packager WH Porter has switched its entire production of up to 40,000 packs a day to a Proseal GT2 tray sealer after the machine demonstrated its ability to cope with tough production line demands.
WH Porter packs all its own fruit, as well as produce from two other growers, to the tune of three million pack units per year. The majority of this is supplied to the multiple retailers under the Angus Soft Fruits banner.

The company had been operating two packing lines, one of which packed fruit into trays with clip-on lids, and the other which used a Proseal GT2 tray sealer to apply a film lid to containers.

As WH Porter’s confidence in the Proseal machine and the heat sealing process grew, the decision was taken to switch the entire crop to heat sealed packs, enabling the business to reduce packaging and the environmental impact of its products.

As Proseal’s Tony Burgess explains, the weight difference between the clip-on lids and the film lids will already have yielded some significant material savings for WH Porter. “While a clip-on lid uses about 8g of plastic, a heat sealed lid only uses about 1g, saving 7g of plastic per container,” he says.

Capable of 90-plus packs per minute with a six-impression tool, the Proseal GT2 is a fully automatic tray sealing system designed to combine high throughput with rapid tool change and compact design. Proseal’s build quality, plus commitment to customer service and support, were highlighted as critical factors in the success of the switch.

James Porter, partner at WH Porter in Angus, Scotland, says: “It is very heartening to see a British company not only achieving such a world-beating standard in build quality, but also backing it up with superb service and support.”