Proper control for ecstatic production

Managing static electricity is important for several reasons of which safety is a leading issue. The most obvious problem can be seen in the operator having to handle the finished sheets. Humans make great conductors and when an operator touches a charged stack or roll of material, or just gets close, the static charge wants to jump to him.

In many cases this discharge can be an annoyance that the operator does not look forward to on a regular basis but realizes that "it's just part of the job." In other cases, it can be a safety concern and, in some unusual operations where laminating or perhaps the introduction of flammable chemicals is added to the mix, this electrical charge can actually be a tremendous safety hazard.

Manufacturing and Feed Problems. Because the material being processed becomes charged with static electricity, it naturally will be attracted to and repelled from just about everything in the manufacturing line.

In cases where the sheets themselves or the waste from the diecut sheets are expected to be cut and then just fall away, this natural attraction can cause some problems. In some cases this will cause jam-ups, while in others it will simply result in contaminated product. In extreme cases, static electrical build-up also can be the cause of problems with electrical control equipment within and around the press or other cutting equipment.

Contaminated Product. Not only does the rectangle or hole being removed from the final part become a problem because of the tendency to 'stick' but slivers of material (caused by cutting or dust that is kicked up when the operator walks around the machine) can cause challenges. All of this oppositely charged material floating around will cause problems with both the production run and quality of the finished product.

Contamination control is a significant issue in film manufacturing environments, especially in critical applications such as food, medical or pharmaceutical packaging. The biggest issue for most manufacturers is that all of these problems resulting from static electricity impact their bottom-line.

Quality problems created by static, like surface contamination, can occur throughout the process, and static control systems offer powerful and flexible solutions to address these problems where they occur. Additionally, high static charge levels on flexible films can result in roller wraps and mechanical feed problems. Discharges from charged film surfaces can cause lockup or unpredictable failures in control electronics or PLCs.

The common areas within the flexible packaging process where static electricity is typically a problem include winders, nip rolls, coating rolls, lay-on rolls, and accumulators.

Flexible films generate static electricity which can become problematic at many points in the application. However, the need for static control is really determined by the critical nature of the application and the stage in the process. For packaging applications, especially where there is a high-end print or coating requirement, static control equipment is generally used from the base film manufacturing process all the way through the final converting stages to avoid quality/defect issues due to contamination. This could include additional applications such as laminating, slitting and winding. Debris on the surface of the film will cause print defects, and can impact coating applications ranging from thickness to clarity if there is an optical requirement.

Trends

Difficult materials are being used in new processes - for example synthetic materials are being laser printed in digital machinery. This can produce enormous static problems - double layer charging - for which there are no easy solutions.

Another trend is the importance of cost for OEMs. Before the recession major OEMs - typically, but not exclusively German machinery manufacturers - thought price was secondary to quality and performance. Now it is often the most important criterion. Quality and performance must be adequate, but the first question now is often "how much is it?".

Very high speeds pose unique and complicated challenges. More power is needed to neutralise the static charge, but thought also has to be given to overcoming boundary layers and the natural air movement generated by fast moving materials.

New developments

One company that has raised the bar in static control is Fraser Anti-Static Techniques who have just launched the NEOS range. The company's director, Bob Fraser , explains why this is such an exciting launch for the market.

"There have been "responsive" static eliminators in the past, but they have been crude systems with simple external sensor rods positioned close to the web downstream of the static eliminator. These sensor rods tried to pick whether there was a charge in the web and relayed this back to the Bar which would output more of the opposite polarity. The rod had to be very close to the material to sense the electric field.

More recently static eliminator Bars have been designed with a second row of emitter pins on the Bar to sense the polarity of the charge in the incoming web. This was expensive and ineffective as the sensors picked up the charge coming from the emitters, rather than the material."

He continues, "NEOS is quite different because it does not need external sensor or additional rows of sensor pins. NEOS technology samples the static charge by comparing the difference in current flowing from the positive and negative emitters on the Bar.

If the static charge is, say, negative it will draw more positive current from the Bar. This tells the Bar to emit more positive ions until the static charge has been neutralised. When the static charge has been neutralised there will be no difference between the negative and positive current flow.

This sampling can be many times a second so the response is very fast. The same sampling mechanism can also compensate for changing distance - so it can work well on winders, for example, where the geometry changes as the reel grows in size."

To put this into context of what this means for converters, there are two major benefits. Bob explains further. " First, there is a huge increase in power available. We had to design and build new monitoring and test equipment at our lab in Bristol to be able to develop NEOS.

"For example, our monitoring equipment works with 10 Nanofarads of capacitance at 25kV. This is 2,500 times more static charge than the industry standard 20 Picofarads at 5kV. It is probably the most advanced development equipment in our industry and was designed with the help of a £20,000 government grant.

"The result is that NEOS is typically 250% more powerful than any competitive equipment on the market.

"Second, NEOS can cope with long range applications. Earlier we mentioned the changing geometry of winders. The NEOS 30 Bar is designed to monitor charges intelligently at distances up to 1m. It works at distances beyond 1m, but at these longer distances the sensing is reduced due to the weaker electric field and the Bar defaults into non-sensing mode."

As to the future, the hope is that advancements such as this technology will provide modern production managers with the ability to pursue and eliminate process variability to improve and ultimately control variability and therefore costs.

This can be achieved without expensive communication and integration with the production machinery. The machine just needs to know that the static has been neutralised.

www.fraser-antistatic.co.uk
www.meech.com
www.simco-ion.com