Static: The invisible influence

Problems with static electricity are increasingly common in the plastics industry; affecting production, reject rates and even health and safety. Here, Stewart Gordon-Smith - Export Sales Engineer at Meech International, manufacturers of static control, air technology and web cleaning systems, writes for BP&R on how to identify problems with static and how best to control it.

Static is a common phenomenon, and one that the majority of us encounter on a daily basis, whether that is through the rubbing of a party balloon on our hair and sticking it to a wall, or touching a object which gives us a short, sharp shock. It is an occurrence that has a real, yet fleeting affect in our day-to-day lives.

However, despite this knowledge of static in everyday life, its effect within industries such as plastics and converting has only become visible in recent years. As machinery speeds have increased and an expanding number of synthetic materials have been developed, the negative effects static can play in industry have become apparent.  

Static electricity causes productivity, quality and safety problems throughout industry: in the form of electrostatic attraction or repulsion, it generates dust contamination and product misbehaviour; as an electrostatic discharge it gives shocks to operators, starts fires and destroys electronic components.

Many factors affect the generation and maintenance of static including humidity, the type of material, repetition and change in temperature. Plastics, in particular, generally maintain static charges for a long time due to their high resistivity, so it is common for problems with static to occur in this industry. Whenever the raw structure of a plastic material is changed, the process will manifest an electrostatic charge, which invariably leads to static problems on the production floor.   

As health and safety legislation has tightened, and consumer expectations and the increasing need for efficiency and cost-savings on the production floor have grown, a need has emerged to resolve these static problems. And to meet this demand, innovative solutions have been developed, often tailored to meet specific requirements.

Companies such as Meech recognised these issues many years ago and came forward to educate and offer solutions for the ‘static problem’. More than 50 years since its inception, Meech’s knowledge of static control is second to none, and not just with regards to the need for static elimination. The generation and application of static plays an equally vital role within the business.

What happens when static occurs in the plastic industry?

As static is generated, process lines begin to mis-feed as products made of synthetic material such as polyethylene, polypropylene and polystyrene misbehave, and the opportunity for contamination of the final product increases dramatically. Add to this the increased potential for serious damage and injury to operators as a consequence of electric sparks generated within explosive environments, and the need to control static levels becomes a fundamental aspect of the production environment. Contamination can spoil finishes of painted products in storage with abrasion issues, and cause rejects in the food, pharmaceutical, automotive and medical industries where quality is of utmost importance.

Over time, the applications and benefits for static elimination and generation have become increasingly diverse.  Below are a couple of specific examples of how static elimination or generation technology can now be applied.

Consider the food and drink industry: a common need for static elimination occurs on a bottling line. First plastic is heated to blow or injection mould the bottle, and then it is cooled dramatically. The cooling process itself generates a huge amount of electrostatic charge. Without static elimination equipment in place, highly-charged bottles would start to stick together, causing line stoppages (loss of production) and mis-feeds; they would attract contamination in the form of dust, make them hard to glue and label, and unacceptable to fill with dust on the inside. As quality of this product is paramount this simply cannot be allowed to happen, so this scenario leads to increased production costs, with additional cleaning at the pre-filling station.

When static is present, belt conveyers are prone to bottles falling over. This can result in damage, increased scrap rates and lower product yield. Static charges on mouldings may cause them to stick to the conveyor belt resulting in the product falling onto the floor not in the collection bin. As mouldings fall into the collection bin the ‘battery effect’ can result in a huge charge being accumulated. This causes a high level of dust attraction and operator shocks. It’s even been known for static to malfunction the electronics in a process line causing it to start to run backwards.

On the other hand, introducing static into a production line can be beneficial: consider synchronising static generation technology with a die cutter on a plastic bag line, a tiny application of static can be applied to the edges of a punched hole. By pinning the area surrounding the handle closed, the static charge effectively prevents the bags from inflating.  Further along the line, static is applied to fix the bags tightly to each other as they are wound into rolls. As a result, the overall size of each roll can be reduced by as much as 30 percent, permitting huge savings in subsequent transport costs.

Despite the invisible nature of static, without the equipment developed to control it, the manufacturing industry couldn’t maintain its health and safety standards and the levels of productivity and profitability that it currently does. In the future, we can expect process line speeds to increase further and become more automated, and the range of materials to expand further. As they do, it will be up to experts in this field to be on hand to offer unique solutions and provide the necessary services to ensure that standards continue to be met with ease.