If you produce PP or BOPP film, you’ll already know how static can affect your production processes. Fast-moving film passing over rollers, through stretching frames and into your slitting and winding machines constantly generates electrostatic charge. It’s a function of how the process works.
Left uncontrolled, this static charge attracts airborne dust and contaminants to the film’s surface, causes layers to cling together on the roll and can create real problems in your downstream print and converting operations. In food and medical packaging applications, contamination on the film surface can have serious hygiene, safety and compliance implications.
So, the question isn’t whether static will build up, but how well you manage it. Antistatic additives are the standard solution, but choosing the right one for PP and BOPP film isn’t as straightforward as you’d think.
In this article, we’ll look at how antistats work, what the main types are, and what you need to weigh up when choosing antistatic additives for your process.
Why are PP and BOPP film prone to static?
Polypropylene (PP) is inherently non-polar and non-conductive. Unlike some other materials, it has no natural mechanism for dissipating electrostatic charge. So, any charge that builds up on the film’s surface tends to stay there.
Processing it into BOPP film makes it worse. Biaxial orientation (the ‘BO’ in BOPP) involves stretching the film rapidly in two directions at high speed, with the film in continuous contact with metal rollers and guides throughout. That combination of high-speed friction and a non-conductive substrate is about as good a recipe for generating static charge as you’ll find.
Static-laden film attracts dust and particulate contamination, which is a serious problem in food packaging and medical film applications where hygiene is a regulatory and quality requirement. It causes film to stick to itself on the roll, which makes handling and slitting more difficult.
And in printing and lamination applications, the film’s surface needs to accept ink or adhesive evenly and consistently. Static charge can interfere with how the ink or adhesive lands on the surface, causing it to spread unevenly, skip or not bond as well as it should. The result can be patchy print quality or weaker laminate bonds.
How antistatic additives work in PP/BOPP film
The antistatic additives used in PP and BOPP film are typically incorporated into the polymer melt during compounding or extrusion, rather than applied as a surface coating at the end.
After processing, the additive migrates from the bulk of the film to the surface. Once there, it forms a thin layer that attracts moisture from the surrounding atmosphere. That moisture layer is conductive enough to allow the electrostatic charge to dissipate rather than accumulate, which is how the antistatic effect is achieved.
There are a few things worth understanding about this mechanism.
First, migration takes time. The antistatic performance develops progressively after the film leaves the line, not instantly.
Second, the biaxial orientation step affects how the additives migrate through the film, which means the additive you choose needs to account for the specific behaviour of the grade in oriented film, rather than its general performance in unoriented PP.
Third, because migratory antistats work by attracting atmospheric moisture, their performance is influenced by ambient humidity. You’ll generally see better antistatic performance in more humid environments, and reduced performance in very dry conditions.
Finally, because the surface layer is gradually depleted through handling, washing or contact with other surfaces, its antistatic performance diminishes over time, which brings us to one of the most important formulation decisions you’ll need to make.
Short-term vs long-term antistats
Not all antistatic additives behave the same way.
Short-term antistats migrate quickly to the film surface and deliver rapid charge dissipation. But because they reach the surface fast, they also deplete faster.
Longer-term antistats are slower to migrate. They provide more sustained protection over time, but they take longer to become active.
For BOPP film, this distinction matters a lot. You need to be able to handle and print on your film quickly after production, so fast-acting antistatic performance is essential in the period immediately after it comes off the line. But your finished packaging also needs to perform through warehousing, distribution and end use, so longer-term antistatic performance matters, too.
A single antistatic additive rarely delivers both. That’s why blending a fast-acting short-term antistat with a slower-migrating longer-term grade is a well-established approach in BOPP film.
The short-term component handles the immediate post-production window, while the longer-term component carries performance through to the end of the product’s useful life.
Getting the right balance between the two will depend on your specific application, line speed and the ambient conditions in your facility and storage environment. There’s no universal starting point that works for every system.
The interaction between antistats and other film additives
Antistatic additives in PP and BOPP film don’t operate in isolation. Your formulation will almost certainly also include slip additives and, potentially, antiblock additives, too. The way these interact with your antistats is worth thinking through.
Some antistatic additives affect the coefficient of friction (CoF) of the film, which has a direct impact on film-to-film and film-to-metal behaviour during winding and converting. If your antistat pushes CoF in the wrong direction, you can end up with handling problems that offset the benefit of better static control. So, choosing an antistat that manages charge without disrupting your target CoF, or validating the combination of antistat and slip agent together, is an essential step in getting your formulation right.
Antiblock additives and antistatic additives generally play different functional roles and don’t directly interfere with each other. But it’s still good practice to validate their performance with all the additives present in your final system, rather than testing each component individually.
Thermal stability is another factor that’s easy to overlook. PP processing temperatures are usually higher than those for PE film, and not all antistatic grades are equally stable under those conditions. So, choosing a grade with adequate thermal stability for your compounding and extrusion conditions will avoid degradation during processing.
What to think about when choosing an antistatic additive for PP/BOPP film
There are several factors worth working through when you’re selecting or reviewing antistatic additives for your PP and BOPP film applications.
Do you need fast antistatic activity post-production, sustained long-term protection, or both? This will determine whether a single additive is sufficient, or whether you need a complementary blend for your application.
Migration behaviour is the next consideration. An additive that performs well in cast or blown film may behave differently in BOPP film, so it’s worth confirming performance in your specific process rather than relying on general characterisation data.
It’s also worth checking how your chosen antistat performs alongside your slip agent and any other additives in the system, particularly how the combination affects CoF and overall surface behaviour. And if you’re processing at the higher end of the temperature range for PP film, make sure the grade you use can handle the heat without breaking down during compounding or extrusion.
If your film is going into food contact packaging, you’ll need to confirm that your antistatic grades are approved for the markets you’re selling into. Commission Regulation (EU) 10/2011 is the starting point for the UK and European markets, but you may have additional requirements depending on where your customers are.
Consistency is the last thing on the list. Antistatic performance is sensitive to variation between grades, so if the quality of your additive quality fluctuates, your film’s performance will, too.
A supplier who can give you consistent specification, solid technical documentation and the regulatory paperwork you need will save you a lot of headaches down the line.
How can MegaChem help?
MegaChem supplies a portfolio of antistatic additives well-suited to PP and BOPP film applications. If you’re working through additive selection, trying to optimise your formulation or looking for alternatives to your current antistats, our team is happy to work through the details with you.
Get in touch to discuss your requirements or request a sample to evaluate in your processes.
