| Copyright (c) 2007 David Banig | | | | because of their nature. This means the material |
| What is slip and how does it work in | | | | is bi-polar and has one end that has a positive |
| manufacturing plastic film and bags. | | | | charge and the other has a neutral charge. This |
| Slip is an organic chemical that is added to the | | | | incompatibility causes the molecule to migrate |
| blend during film extrusion process to modify the | | | | referred to as bloom through the polymer to the |
| coefficient of friction (COF). COF is a | | | | surface of the plastic film. |
| measurement of the amount of friction between | | | | The migration of slip to the surface of the |
| two surfaces as they begin to slide and as they | | | | material the lower the COF and more slippery the |
| continue to drag against one another. The amount | | | | plastic film becomes. The COF relates to |
| of energy it takes to put an object in motion is | | | | packaging because the substrates used to |
| always greater than the amount of energy that it | | | | package objects always come in contact with |
| takes to keep it moving while it is in motion. | | | | other surfaces or themselves. As most packaging |
| Although there are a number of chemicals that | | | | operations are very high speed, COF plays a very |
| are used to modify the COF the two main ones | | | | large role. The packaging material must have just |
| used in Polyethylene and Polypropylene are | | | | the right COF in order to track properly on the |
| Erucamide (which is considered a slow bloom) and | | | | packaging machines. If a material is too slippery |
| Oleamide(which is a fast bloom). The materials are | | | | the film will not track properly and may cause |
| sometimes called primary amides. Typically 500 to | | | | issues such as bad sealing or cause a powder |
| 1500 parts per million (PPM)of slip is a very | | | | substance that builds up on the tracking rolls which |
| efficient molecule to be added to plastic film in | | | | will cause packaging failures. When the plastic |
| very low concentrations.The slip additive can be | | | | material becomes sticky it can have the opposite |
| let down at the levels of 1 to 3% by weight in | | | | effect. It may not allow the film to un-wind |
| blending while extruding the plastic film. Slip | | | | properly and cause web brakes or other tracking |
| molecules are very low in molecular weight as | | | | problems. Either scenario can shut a packaging line |
| compared to the polymer in which they are used. | | | | down. |
| These molecules are somewhat incompatible | | | | |