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Achieving Zero Defects In Packaging Seal Quality. Abstract: Many products are packed in sealed containers and in many occasions with a protective gas, to maintain and enhance the quality of the product until it at least reaches a use by date. Poor packaging seal quality then inevitably leads to customer complaints, and a reduction in customer confidence especially when dealing with the larger retailers. As there are many reasons for leaks it is not possible to eliminate them totally, but with the use of reliable and robust leak detection, the occurrence of leaking packs can be drastically reduced and prevented from reaching the retailer / customer. Piotec Ltd is an engineering company with many years experience in problem solving and leak detection that has developed a range of machines to test packaging for micro leaks. Through a combination of leak detection and process improvement driven by information coming from the leak detection machine, Piotec customers are able to achieve almost zero seal defects leaving their premises and reduce losses due to leaking packs. Sealing and causes of leaks Each packaging user has their own defined reason for keeping their product sealed, some use Nitrogen as an inert gas to keep oxygen out, others such as red meats are packed in an Oxygen rich environment to keep the meat looking red and appetising, and carbon dioxide to restrict bacterial growth. All these packs are only then successful if the internal environment is maintained and the gas is contained and external contaminants kept out. In a normal working environment it is impossible to control every element that could affect the seal quality, contamination, material quality, sealing parameters and normal packaging issues such as creasing in the formed packaging materials. Sealing Conditions:

o Contamination.

Each sealing process has the potential to have product in seal contamination issues. Horizontal Flow Wrap can have issues were particles of the product have fallen on to the material and land in the seal area, or can be blown into the seal area with the purge pipe. Vertical Form Fill and Seal where some of the product is either stuck to the side on the formed tube, or is still falling through when the sealing jaws close on the material. Thermoformed and tray sealers can also have product particles landing on the flat seal face prior to sealing, or thinning of the material at corners. A range of measures can be

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introduced to minimise this contamination including particle removal using air knives, anti-static measures and better control over the filling process.

o Packaging Film Quality. There are probably 2 main issues in this area at present, one is price, quite simply the better the seal ability and robustness of the material the more expensive it is. The second is the drive to reduce and minimise the packaging material used. As most packaging materials are a combination of at least two materials and an adhesive layer to hold them together, the quality and control of this manufacturing process can have a big influence on the quality and reliability of the final packaging. Poor process control can obviously affect the quality of each layer in the film, the thickness and uniformity of each layer, the strength of the bond between them and finally how they are wound on to a core ready for delivery to you the customer. Sealing Parameters: In order to create a seal between two pieces of material there are three parameters at work, Time, Pressure and Temperature.

Time Time is normally controlled by the throughput of the machine and can normally only be adjusted by slowing the speed of the packaging machine, so it is usually the last resort when trying to improve seal quality.

Pressure. Pressure is adjustable and can play a vital part in the quality of the seal, too little pressure and the material is not well bonded, too much pressure and the material can be damaged. This is also complicated by high points in the seal at overlaps in Vertical Form Fill and Seal or Horizontal Flow Wrap where the longitudinal or fin seal is sealed in the end seal.

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Demonstration of packaging film in a horizontal flow wrap.

Upper Seal Tool

Lower Seal Tool

Packaging Film

Distance along seal tool

Pressure

The pressure profile is uneven especially at both sides of the overlapping fin seal. This low-pressure area is where leaks are most likely to occur. If the seal tool mechanism is worn or not sufficiently robust then this problem can be made worse as in the following demonstration.

Distance along seal tool

Pressure

Lower Seal Tool

Upper Seal Tool

Packaging Film

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The rock or float in the seal tool will mean that the tool will apply more pressure to one side leaving the opposite side with little or no pressure. Again creasing will also play a vital role in the pressure profile, as in the example to follow of a pack with a crease on one side.

Distance along seal tool

Pressure

Lower Seal Tool

Upper Seal Tool

Packaging Film

Areas of low pressure will be more prone to not having proper seal adhesion so small vents can appear through the seal at these points. Areas of high pressure can cause packaging damage, de-lamination of the packaging layers and ruptures. One useful method of checking this pressure profile is using pressure paper, which makes a colour imprint depending on how much pressure is applied. When this is inserted into the seal tool with the packaging material in place, it will show the pressure profile clearly.

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Temperature. The heat required to melt the sealing layers so that they are totally melted and fused together, comes from the seal tool. Due to the small amount of time the seal tools are closed on the packaging material and the fact that plastics are poor heat conductors, the tool temperature is usually much higher than the melting temperature of the sealing layer. This is why the tools are retracted well clear of the packaging material during the cycle. There is a fine balance between tool temperature, material thickness and seal times.

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As the sealing machine is running each time the sealing jaws close on the packaging material, heat is transferred to the material from the sealing tools. This heat is then replaced by the heater cartridges. Poorly wound cartridges can generate more heat in the centre and less towards the outside; this causes a temperature profile across the seal tool.

Upper Seal Tool

Lower Seal Tool

Distance along seal tool

Temperature

Progressively wound seal tools will give a much more evenly wound temperature profile. In order to check this profile, a thermo couple can be fitted to a number of points along the tool and the temperature recorded as the machine is running. It is important to record the temperature as the machine is running at full cycle speed. Process anomalies and controls. When the seal tools close on the material, the temperature increases to melt the inner sealing layer. As the tools open, the inner sealing layer is still molten with little or no strength of adhesion, so any stress on the material at this point will cause the layers to move relative to each other as they are cooling, which leads to a weakening of the sealing layer and increases the chance of a leak occurring.

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Seal tool cleanliness. Contamination on the seal tool face - especially a build up of material that has been extruded from the packaging film as it is sealed, will stick to the tool face and remain molten and tacky. Each time the seal tool closes on the film, this contamination will try to pull the joint open as the seal tool opens, and the sealing layer is still soft and weak.

Upper Seal Tool

Lower Seal Tool

Regular scheduled cleaning will prevent this build up causing leaks.

Web Tension. Again as the seal tool opens, the seal layer is at its weakest and most susceptible to damage. Uneven or varying web tension can cause the material to snag or tug as the pack separates from the main film, especially in Vertical Form, Fill and Seal or Flow Wrap processes. This increase in tension or stress on the molten joint, can cause an increase in the likelihood of a leak occurring as the molten layers can separate.

Extruded contaminant

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Creases. As mentioned previously, creases will cause an uneven pressure profile and therefore increase in the probability of small vents forming adjacent to the overlap.

VENTS

Before sealing

After sealing

Inner Sealing layer

Outer Layer

Inner Sealing layer

Outer layer

Adjusting the web tension, optimising pack length and seal tool positioning can minimise the creasing but will not totally remove creases.

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Measuring and eliminating leaks In order to monitor and control the seal quality, an accurate leak detection method is required. Piotec Ltd has developed and patented a range of leak detection machines based on vacuum force technology, that is capable of detecting micro leaks at least down to 10 micron in a sealed pack, without doing any damage and irrespective of the gas type inside the pack. There are 3 main machine types available. Seal Solo, which is an Offline machine that is manually loaded by an operator. Seal Random, which automatically picks one pack at a time from the line, tests it and returns good sealed packs, there by removing the need for an operator. Seal Plus, which tests every pack coming from the sealing machine and automatically removes leakers. Seal Solo: Offline Testing

These machines are used for both continual sampling from the production line where an operator removes a pack, tests it and returns it to the line, and batch testing where a sealing parameter is changed, then the subsequent batch is tested to check on the occurrence of leaking packs. This machine stores the information for both quick access through a HMI, and a downloadable file for more in-depth analysis, as each test result is stored along with the time it was tested and the severity of the leak.

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Seal Random: Random Sampling A random sampling machine that automatically removes packs from the line, tests it and returns the pack to the line if it is well sealed. This machine removes the dependence of an operator to load and unload the machine during normal production, and can test two packs every minute and therefore builds up a clear picture of the process capability, and any subsequent changes in the process condition.

Seal Plus: Inline 100% inspection. This machine will test every pack coming from the sealing machine, automatically removing any leaking packs. The Seal Plus machine will monitor the occurrence of leaks, and trigger a set of alarms for increasing leak rates to a point where it can stop the line, if the occurrence of leakers reaches a critical pre-set limit. The machine stores information on each leak including time produced, leak rate and the count interval, this information can then be analysed to monitor and drive process improvement.

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Comparison of each leak detection methods:

1. Confidence that no leaks will reach the customer.

Confidence

100%

Offline Random Sampling Inline 100%

Inline leak detection has been proven on many occasions to remove all leaking packs with 100% accuracy, but as there is subsequent handling and transportation it is imprudent to say that no pack reaching the customer will be leaking.

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2. Volume and accuracy of information to help drive process improvement.

Offline

Volume & Accuracy

Random Sampling Inline 100%

of information

As every pack is tested with inline leak testing, this provides the maximum information. Random sampling provides a high level of consistent information based over a longer running period, while offline testing relies heavily on an operator to keep sampling the product, therefore the sampling is less consistent and not as accurate

3. Response time to changes in rate of leak occurrence.

Offline

Response time

Random Sampling Inline 100%

Again as the inline machine is sampling every pack, any changes in the process capability are very quickly detected, thereby minimising waste. Random sampling will build up a clear picture over a longer running time of the process capability; but any sudden changes in seal quality will take longer to spot. Offline testing will be less responsive than the Random Sampling machine and again reliant on the operator continually loading samples for testing.

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4. Cost, Integration and Floor Space.

Offline

Cost, Integration

Random Sampling Inline 100%

Floor Space

The Offline machine is a ‘stand alone’ machine requiring a simple singe phase power supply and requires a very small footprint. The Random Sampling machine is a compact machine that is installed adjacent to the product line, and normally requires minimal integration, usually just modification to a conveyor’s side guides, while the inline machine is fully integrated into the line and requires more space, planning and is more expensive.

How Leak detection is used to reduce complaints, waste and subsequent costs. The occurrence of leaks fall into two categories, the first is leaks that randomly occur during a normal packaging run, and which are a measure of the overall process capability. These leaks cannot normally be attributed to any fault condition and occur at random intervals through the production run. The other type of leaks are caused by a fault condition and are more recognized as a cluster of leaks or a stepped increase in the occurrence of leaking packs. Examples of random leaks would be product falling into the seal area, slight changes in the process conditions due to inconsistent running of the line, or a heavy crease forming in the packaging material and then disappearing again. Variation in film quality and general overall film quality will also produce random leaks through a run. Clusters or stepped increases in leak occurrence can be a result of a failure in a heating element, failure of a thermocouple or a component failure, though these will need intervention to correct the problem. Contaminations build up on seal tools and web tension problems will create clusters of leaks that can appear and disappear during a production run.

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Offline Sampling: Seal Solo In an offline sampling regime using a Piotec Seal Solo, the overall production capability can be measured. On an average line running at a throughput of 80 packs per minute, a well-managed sampling regime could sample 1 % of the product, which in an eight-hour shift could produce a sample size of 300 packs per shift. This will give a fairly good indication of the process capability, and be useful as a reference point from shift to shift performance. As the information can be stored and analysed, the overall process capability can be monitored and improved, as changes in production set up and parameters can be monitored on a shift bases. This equipment is also useful for batch process monitoring, where a parameter or film change is followed by a batch test to compare the previous to post change performance. Clusters of leaks can obviously be missed totally, but stepped increases can be spotted. Actual downloaded file showing result of testing and leak and occurrence.

Date Time Pass/fail Fail Point Date Time Pass/fail Fail Point

11/22/2010 10:15:02 1 0 12/01/2010 10:35:28 1 0

11/24/2010 08:35:06 1 0 12/01/2010 10:36:00 1 0

11/24/2010 09:22:16 1 0 12/01/2010 10:36:30 1 0

11/24/2010 09:33:28 1 0 12/01/2010 11:54:18 1 0

11/24/2010 10:47:52 1 0 12/01/2010 11:54:44 1 0

11/24/2010 10:49:20 1 0 12/01/2010 11:55:14 1 0

11/24/2010 11:17:32 1 0 12/01/2010 11:55:46 1 0

11/24/2010 11:18:12 1 0 12/01/2010 12:15:04 1 0

11/24/2010 11:42:00 1 0 12/01/2010 12:15:36 1 0

11/24/2010 11:48:54 1 0 12/01/2010 12:16:06 1 0

11/24/2010 12:16:00 1 0 12/01/2010 12:16:38 1 0

11/24/2010 12:22:52 1 0 12/01/2010 12:21:08 1 0

11/24/2010 12:51:10 1 0 12/01/2010 12:21:38 0 30

11/24/2010 12:51:54 1 0 12/01/2010 12:22:10 1 0

11/28/2010 08:52:00 1 0 12/02/2010 08:34:50 1 0

11/28/2010 08:52:44 1 0 12/02/2010 08:39:12 1 0

11/28/2010 10:02:54 1 0 12/02/2010 09:10:38 1 0

11/28/2010 10:03:22 1 0 12/02/2010 09:23:38 1 0

11/28/2010 10:28:36 1 0 12/02/2010 09:24:30 1 0

11/28/2010 10:29:20 1 0 12/02/2010 09:44:48 1 0

11/28/2010 11:27:42 1 0 12/02/2010 10:04:26 1 0

11/28/2010 11:28:10 1 0 12/02/2010 10:05:06 1 0

11/28/2010 15:42:00 1 0 12/02/2010 11:03:46 1 0

11/28/2010 15:43:00 1 0 12/02/2010 11:06:36 1 0

11/28/2010 18:52:44 1 0 12/02/2010 12:20:30 1 0

11/28/2010 18:54:02 1 0 12/02/2010 12:21:30 1 0

11/30/2010 08:36:20 1 0 12/02/2010 12:43:26 1 0

11/30/2010 09:01:00 1 0 12/02/2010 12:44:14 1 0

11/30/2010 09:01:46 1 0 12/03/2010 09:39:24 1 0

11/30/2010 09:32:52 1 0 12/03/2010 09:39:52 1 0

11/30/2010 09:33:28 1 0 12/03/2010 11:34:32 1 0

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The fail point column can be used to estimate the size of leak in a failed pack. Random Sampling: Seal Random The effectiveness of the offline leak detection is very much reliant on an operator continually sampling packs during a production run and maintaining this discipline during the full production run. The random sampling machine removes this requirement by continuously sampling product automatically and removing the subjective nature of a person loading the machine. A person will not test a pack that is clearly leaking, as they know it will fail, thereby distorting the true profile of a production run, while a machine will collect the sample and report the result objectively. As the sampling regime is more thorough than offline testing, any changes in the occurrence of leaking packs could be used to trigger alarms. Small clusters of leaking packs can again go unnoticed. Due to the higher numbers of packs tested the information on leaks is stored rather than every test. Typical sampling record. Date Time Fail Pt. Count Date Time Fail Pt. Count Time Fail Pt. Count Count

03/08/2011 10:13:20 20 2 03/08/2011 12:45:08 24 2040 15:37:56 36 16938 5388

03/08/2011 10:15:32 35 66 03/08/2011 12:47:44 49 2082 15:50:00 29 17178 5628

03/08/2011 10:17:32 46 120 03/08/2011 12:48:06 57 2088 15:54:54 59 17292 5742

03/08/2011 10:18:38 23 150 03/08/2011 12:52:06 37 2148 16:01:06 36 17436 5886

03/08/2011 10:20:24 25 198 03/08/2011 12:55:18 29 2214 16:12:44 21 17694 6144

03/08/2011 10:26:36 26 366 03/08/2011 12:59:18 29 2292 16:13:32 15 17712 6162

03/08/2011 10:39:50 58 726 03/08/2011 13:04:08 55 2388 16:21:36 27 17898 6348

03/08/2011 10:41:22 37 762 03/08/2011 13:05:20 27 2412 16:30:34 54 18102 6552

03/08/2011 10:44:38 55 834 03/08/2011 13:07:48 28 2460 16:48:00 29 18504 6954

03/08/2011 10:45:32 45 858 03/08/2011 13:08:40 43 2478 16:55:58 11 18690 7140

03/08/2011 10:45:44 49 864 03/08/2011 13:12:02 21 2532 17:01:20 58 18816 7266

03/08/2011 10:47:04 39 900 03/08/2011 13:13:36 10 2562 17:05:10 43 18906 7356

03/08/2011 10:48:12 35 930 03/08/2011 13:14:26 34 2580 17:09:54 26 19014 7464

03/08/2011 10:48:24 29 936 03/08/2011 13:17:12 56 2640

03/08/2011 10:51:30 10 1020 03/08/2011 13:28:02 35 2868

03/08/2011 10:52:22 20 1044 03/08/2011 13:39:50 39 3144

03/08/2011 10:55:46 45 1074 03/08/2011 13:41:22 54 3180

03/08/2011 10:56:56 28 1086 03/08/2011 13:45:12 40 3270

03/08/2011 10:59:42 55 1158 03/08/2011 13:45:28 58 3276

03/08/2011 11:00:36 38 1182 03/08/2011 13:54:10 33 3480

03/08/2011 11:07:12 46 1356 03/08/2011 14:01:36 56 3648

03/08/2011 11:09:00 45 1404 03/08/2011 14:14:36 21 3948

03/08/2011 11:23:44 39 1506 03/08/2011 14:16:08 56 3984

Inline Leak Detection: Seal Plus

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Inline or 100% leak detection has a number of key advantages as it is testing each individual pack leaving the sealing machine. Not only is every leaking pack removed from the production line, but also the information collated is a 100% picture of the process and every change in the process. The Piotec Inline Seal Plus machine is the only 100% inline leak test machine on the market that tests each individual pack. The test method used allows the machine to test packs and record the results, and at the same time reject packs at a preset leak rate limit. If for example a customer required only leaks greater than say 50 micron to be rejected the machine can be set up to do this. As the Piotec machine is testing every pack individually, the machine can instantly recognise any changes in the process leak rate. The occurrence of leaks and any changes will trigger a set of alarms, from an initial alarm to say that the leak rate has risen to a final alarm that will stop the sealing machine should a major increase in the occurrence of leaks arise. This will greatly reduce the amount of waste produced when something fails in the sealing process. Since the inline machine is testing every pack coming from the sealing machine, the amount of information collated is huge, so again only information on the leaking packs is stored for analysis. Typical Example of an inline downloaded record. Date Time Count Date Time Count

02/02/2011 00:10:12 258 02/02/2011 00:22:50 582

02/02/2011 00:10:24 264 02/02/2011 00:23:04 588

02/02/2011 00:10:52 276 02/02/2011 00:23:16 594

02/02/2011 00:11:18 288 02/02/2011 00:23:30 600

02/02/2011 00:11:42 294 02/02/2011 00:23:44 606

02/02/2011 00:12:38 318 02/02/2011 00:24:10 618

02/02/2011 00:12:50 324 02/02/2011 00:24:24 624

02/02/2011 00:13:04 330 02/02/2011 00:24:50 636

02/02/2011 00:13:18 336 02/02/2011 00:25:44 660

02/02/2011 00:13:44 348 02/02/2011 00:26:22 678

02/02/2011 00:13:56 354 02/02/2011 00:26:36 684

02/02/2011 00:14:50 378 02/02/2011 00:27:02 696

02/02/2011 00:15:16 390 02/02/2011 00:27:16 702

02/02/2011 00:15:30 396 02/02/2011 00:27:28 708

02/02/2011 00:15:56 408 02/02/2011 00:27:42 714

02/02/2011 00:16:22 414 02/02/2011 00:27:56 720

02/02/2011 00:16:48 420 02/02/2011 00:28:22 732

02/02/2011 00:17:06 426 02/02/2011 00:31:00 744

02/02/2011 00:17:18 432 02/02/2011 00:31:36 756

02/02/2011 00:17:32 438 02/02/2011 00:32:24 768

02/02/2011 00:17:46 444 02/02/2011 00:32:36 774

02/02/2011 00:18:24 462 02/02/2011 00:33:30 798

02/02/2011 00:18:38 468 02/02/2011 00:33:42 804

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This information can then be trended and used for comparison of shift to shift changes, or leak rate during the day, packing film changes etc. If this data is then graphed as leaks against the number of packs tested a very useful picture of the process arises as in the following real life example.

Plot of interval between fails Vs time.

At 23.30 it can be seen that there is a lot of leaks, then something is done and the subsequent production shows a big increase in the intervals between leaks. It was later found that the seal tools were cleaned, which lead to seal tool cleaning being implemented on a two hourly preventative maintenance schedule.

Conclusion. There is a conflicting set of pressures on packaging companies to improve the shelf life and quality of their products and at the same time reduce the amount of packaging used. This is driving the need for greater process control and overall understanding and monitoring of sealing processes. It then makes sense that only by having an accurate and robust leak testing machine or regime, can a company hope to drive process monitoring and control and there by meet the needs of the current market. Every process will produce leaking packs even when the process is running at optimum conditions. There is a wide range of fault conditions that can cause leaking packs, so leaks will always occur in a process, depending on the product, its shelf life and the nature of the customer / retailer, and a decision has to be made on the complexity and suitability of the leak test regime. If the product has the potential to make the end user ill, or there is potential for a major product recall, then an inline solution will remove these

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risks and at the same time reduce the occurrence of leaks in the process, through continuous process monitoring and improvement. If the product is not so critical then a random sampling regime may well be sufficient, but there is always the risk of clusters of packs going out undetected and by their very nature as a cluster, they can all land on one retailer shelf at the same time, distorting the retailers view of the size and scale of the leak problem.