Extrusion coating can be easily defined as a process which is used to coat the thermoplastic material onto a substrate like paperboard aluminum foil, woven fabric, paper, PET, BOPP film etc. Most commonly used resins in this process are various polyolefins such as ethylene vinyl acetate copolymers, polyethylene, ionomers, and polypropylene. For instance, this process is used for improving the features of paper by coating it with polyethylene, making it a better water resistant.
Process Of Extrusion Coating
The process of extrusion coating includes coating of a substrate with precisely metered film of molten plastic. The thin extruded molten film is pulled down onto a substrate and then into the nip which is amidst the pressure roll and chill roll, below the die. There is a specific amount of pressure in between these two rolls and this pressure forces the plastic onto the surface. This surface is moving at a speed which is faster as compared to the extruded film and the drawing of film onto the desired thickness. The entire extrusion coating line includes Extruder, Die, Chrome Plated Chilled Roll, Back Up Roll, and Winders / Unwinders.
Advantages Of Extrusion Coating
Factors Influencing Coating Performance
In the extrusion coating process, various resins are used and the entire processing is dependent on various factors that are as follows:
- Melt Temperature
- Die Gap
- Air Gap
- Chilled Roll Temperature
For extrusion coating, the resins must have some special characteristics like higher melt index (to ensure better adhesion), free from additives, and ideal amount of antioxidants. In addition to these, there are a couple of other characteristics that must be present in the resins; these are reduced neck-in properties and good adhesion to substrate at higher line speeds.
Applications Of Extrusion Coating
The extrusion coated products are wide used in the segment of synthetics woven sacks. These are also used for coating on the non-raffia substrates that primarily includes coating on Al-foil, Paper, PET & BOPP substrates. The major application areas of extrusion coating are as follows:
- Woven sacks for fertilizer packaging
- Coating on conventional jute bags
- Soap wraps
- Pharmaceutical strip packaging
- Cable wraps
- Coating on paper used in packaging of salt and sugar (sachets)