Have you ever had difficulties in separating a film? or have you observed that dust easily adheres to its surface? These problems are frequently found in polyethylene or polypropylene films, even though most of these resins manufacturers must have already incorporated additives to reduce and even eliminate these complications. As a result, film manufacturers find it necessary to use masterbatches with slip, antistatic or antiblocking agents to eliminate such inconveniences. Below you will find a brief description of how these additives act and the references you can obtain from Comai.

Slip masterbatches are added to polypropylene and polyethylene films to improve the film sliding over metal surfaces or over a parallel film surface.

Decreased Coefficient of Friction is the result of the slip additive migration to the film surface due to the incompatibility of the slip additive and the polymer.

The following graphic shows the variation of a polypropylene film Coefficient of Friction when a slip masterbatch is added, depending on the manufacturing time.

Comai offers two basic references of odorless and tasteless slip additives which will not present printing or sealing problems with a dose of 1 – 4%.

• 721-1 NT for Polypropylene films

• 721-2 NT for Polypropylene films

Statics is generated by friction between two bodies. It leads to processing difficulties (blocking, dangerous electrical charges, printing problems, etc.) and end user troubles (blocking, dust accumulation in the surface). The solution is to incorporate antistatic additives that will act directly and internally in the polyethylene or polypropylene processing.

Internal antistatic masterbatches work by generating a conductive path to attract the charged molecules which migrate to the film surface and form a uniform layer where the hydrophilic part of the additive reacts to the water molecules of the surface and lowers the surface resistivity. This value determines how much a given product is charged.

There are fast- and slow-migration antistatic additives. Comai offers the benefits of both types of additives with its 745-2 AS masterbatch for polypropylene films and 745-4 AS for polyethylene films. These materials offer the advantages of fast migration for the internal use of manufacturers (extrusion and subsequent printing or sealing) and slow-migration for the end user, to obtain dust-free surfaces over extended periods of time.

The following graphic shows MB 745-2 AS antistatic behavior in 50-micron polypropylene films, over the time.

Antiblock masterbatches are used to reduce the strength needed to separate the two layers of a film. In some cases the film surfaces adhere with each other (blocking) making it difficult to open the bag. Blocking is due to pressure or temperature reasons.

Comai’s additive masterbatches include three basic types of antiblock masterbatches.

• 733-1AB Antiblock, PP & Synthetic Silica base. Applications: high transparency films and when the maximum effect of this type of additives is required; application percentage between 0.1 and 3%.

• 733-2AB and 733-3AB Antiblock LLDPE & Synthetic Silica base. Applications: high transparency films and when the maximum effect of this type of additives is required; application percentage between 0.2 and 1%.

• 735-1AB Antiblock LLDPE & Talc base: Applications include opaque and medium action films; application percentage between 0.2 and 1%.

• 750-3NT Antiblock LLDPE & Calcium Carbonate base. Applications include opaque and low action films.