Plastic Film

The main reason a certain type of plastic is chosen as a food packaging is to protect the product. A different type of plastic may hold a larger static charge but may fail to protect the product contained within it (or even contaminate it as the packaging degrades)

Have you looked into the Triboelectric effect and static electricity theory and generation.

http://en.wikipedia.org/wiki/Triboelectric_effect

http://en.wikipedia.org/wiki/Static_electricity

I remember seeing somewhere that plastic packaging was intentionally charged to prevent the plastic packaging sticking on the packaging machine.

There should be some data sheets available on the internet covering Triboelectric properties of various plastics. A quick search produced the following.

http://www.ami.ac.uk/courses/topics/0214_ee/index.html

Be aware that there are a number of variables that will effect the overall maximum charge holding and dissipation over time.

What's the application exactly?

I can't answer specifically to plastic films, but I know a bit about plastic particles. The average toner in a copier is either a styrene-acrylate or polyester thermoplastic, 8 - 12 um. In the "copying" process, quality of reproduction is dependant on several factors, but one of the most significant is the "charge" and charge distribution of the plastic toner particles, as the process is based upon electrostatics and potential / bias. Still today the thermoplastic resins are designed and selected mainly based upon their thermal characteristics, balancing ease of fusion to paper at high rates with minimal heat / pressure and the ease of "crushing" to the optimal particle size distribution, and not based (so much) on the inherent "charge-ability" of the plastic polymer itself. Generally, the toner particles develop their tribo-charge in the developer unit, where the the toner is vigorously mixed with a "developer". The key to developing the proper charge is based upon the two materials (toner and developer) and where they relatively stand on the triborlectric series. Where they are relatively positioned will determine which material will be "positve" and which will be "negative" and the further removed from each other, the greater the generated charge. As the plastic polymer was chosen mainly for its thermal characteristics, it must then be tuned to the proper charge level and polarity. This is done by a combination of two methods; incorporating a small amount (0.5 - 5%) of charge control agent (CCA) in the polymer prior to crushing, and surface treatment of the crushed toner with a small amount (0.05-0.5%) of a nano-sized material (0.05-0.5%). Yep, the toner folks have been into "nano" for decades! The CCA is usually a metal complex dye, and the additive is typically a treated silica, either fumed or precipitated, but can be floropolymers, magnetites, carbon blacks, and even oils. The leading edge manufacturers are now desgning most of the charge characteristics into the polymer / copolymer itself, minimizing issues of CCA dispersion in the plastic, as well as avoiding use of a metal complex dye (some are hazardous, even banned in regions, i.e. Chromium based). There are dozens of easily searched patents, and some technical lit on the web if you search charge control agents / CCA. You may even want to search out the triboelectric series. What must be kept in mind is that the triboelectric charge is completely relative, and is wholly dependant on the "other" material, like application rollers, the aforementioned "developer", your skin, etc. Now, you can also consider the alternate to tribo-charging...and that is corona charging, as used in most (but not all) powder coating applications, but that must be left for another time...

In the plastic film business we are mainly concerned with dissipating static charges in the film. As "Jack" said, in almost all of our machines we hit the film with a static charge, to neutralize the elctricity that built up in the film during processing.

My experience in polyethylene films would say that the higher the density of the plastic, the higher the tendency to build and retain static charges. Probably due to the linear alignment of molecules. When we combine polythylene with nylon, the effect is even greater.