4.1 Antiblocking Agents

Antiblocking agents are used in the packaging film industry to stop film from sticking to itself during processing, when in use, or during storage on rolls or shipped in cartons. Elevated temperature, pressure, and processing time all increase the tendency to blocking. This is potentially expensive because poor behaviour on processing lines can lead to costly interruptions in production, together with static build-up. The affected film may be destined for the manufacture of supermarket bags, rubbish sacks and bags for industrial merchandise, freezer food, garments etc.

The majority of antiblocking agents are used in LLDPE and PP because of the very high volumes produced. There is also a demand for them in flexible PVC, and to a lesser extent in hard films like PET.

The mode of action of particulate mineral antiblocking agents is illustrated in Figure 4.1. The force resisting the sliding of two contacting film surfaces over each other is much greater when the surfaces are smooth (and therefore in intimate contact over a wide area) than when they are rough. The role of antiblocking agents is to roughen the film surfaces slightly, which is achieved by the additive particles protruding out of the film surface, so that the surfaces are in contact with each other at fewer points.

Figure 4.1: Principle of antiblocking agents: the particles protrude beyond the film surface, reducing the effective contact area between adjacent film layers
After E.M. Abdel-Bary, Ed., Handbook of Plastic Films, 2003, Rapra Technology Ltd.

The preferred...