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Why to use slip agents ?
Due to a high coefficient of friction, polyolefin films tend either to adhere to themselves or to the production equipment during film processing.
Slip additives modify the surface properties of polyolefin films and reduce the film to film friction (e.g. on a roll) and the friction between the film and other surfaces with which they come into contact.
Slip agents therefore:
- facilitate increased line speed in the manufacturing process
- enhance packaging machine operations due to reduced CoF (coefficient of friction) values
You will find out what are the principles of action, what types of slip additives are commonly used for polyolefins and what is their structure and finally, how friction between films or between film and production/packaging equipment can be reduced. To help you to find the right slip agent for your desired application, we are offering practical recommendations.
Principle of action
Slip Effect is a term used to describe the sliding of parallel film surfaces over each other or the sliding of film surfaces over substrates. Slip agents - such as stearamide, oleamide and erucamide - are added to polyethylene (PE) or polypropylene (PP) films during the extrusion process to decrease friction - both film-to-film friction and that between the film and production equipment - in order to increase the output of the line and to improve packaging line operations. Slip effect is measured as CoF (Coefficient of Friction).
Decreased CoF is a result of the migration of slip additive to the film surface due to the defined incompatibility of the slip additive with the polymer. The migration speed of slip agent to the surface is largely decided by the additive's chain length (compatibility with the polymer) and the crystallinity of the polymer. The larger the slip agent (more carbon atoms) the more compatible it is with the polymer and the slower it migrates. So oleamides migrate faster than erucamides.
Erucamides are more heat stable than oleamides, more resistant to oxidation and create fewer volatiles during processing. This means that erucamides are more suitable for higher processing temperatures and processes with high output, which will result in high quality final products. Structurally, PE is less crystalline than PP, so encourages faster migration of the slip additive.
Due to the migration of the slip agent to the surface of the polyolefins, primary amides are not only used as slip agents for polyolefin films but are also recommended for use as demoulding agents in injection moulding applications.
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