Calendered Films
Written October 16, 2019
Like cast, calendered film also gets its name from the manufacturing process. The production of calendered film is similar to mixing and rolling out pie dough. It is formulated with similar raw materials as cast vinyl. These 'ingredients' are mixed and later 'kneaded' in the extruder. Instead of grandma's rolling pin, gigantic heated, steel rollers form the vinyl into a thin sheet. This process is called 'calendering'.
The first step is 'paste mixing' and 'extrusion': here all raw materials (e.g. PVC powder, liquid softener, colors) are mixed together based on the formulation. Improved formulations and the use of new pigments lead to increased color options for calendered film. In the extrusion process the prepared fine powder mix ('dry blend') will fuse together into a homogenous mass, called the melt.
The next step - the mill - consists of two counter rotating rolls, which can be heated up to 350 °F. The melt is continuously pulled into the gap and flattens out due to the pressure and temperature that is applied by the mill rolls. When the strip reaches the calender rolls, it passes between multiple gaps, which increase the temperature and uniformity.
After each gap the film becomes thinner and wider according to the specifications. The film is still heated when it reaches the embossing station where different pattern and gloss levels are applied to the film. Each surface structure requires a different embossing roll - e.g. to produce a high gloss film a different embossing roll is required but also a special setting of the whole calender line. Now that the film has received its final dimensions and surface it needs to be cooled down and transported to the last process stage of winding.
The first step is 'paste mixing' and 'extrusion': here all raw materials (e.g. PVC powder, liquid softener, colors) are mixed together based on the formulation. Improved formulations and the use of new pigments lead to increased color options for calendered film. In the extrusion process the prepared fine powder mix ('dry blend') will fuse together into a homogenous mass, called the melt.
The next step - the mill - consists of two counter rotating rolls, which can be heated up to 350 °F. The melt is continuously pulled into the gap and flattens out due to the pressure and temperature that is applied by the mill rolls. When the strip reaches the calender rolls, it passes between multiple gaps, which increase the temperature and uniformity.
After each gap the film becomes thinner and wider according to the specifications. The film is still heated when it reaches the embossing station where different pattern and gloss levels are applied to the film. Each surface structure requires a different embossing roll - e.g. to produce a high gloss film a different embossing roll is required but also a special setting of the whole calender line. Now that the film has received its final dimensions and surface it needs to be cooled down and transported to the last process stage of winding.
From the extruder to the winder a calender machine can be 90 feet long. Due to improvements made in the manufacturing process, calendered film can be produced as thin as 2.0 mil, and can have quite a degree of conformity (ability to bend). The quality of calendered films can range from economy, which use a monomeric plasticizer, to a high-grade, which would use a polymeric plasticizer. The durability of calendered films can range from one year up to seven years.
Advantages of calendered films:
- Today's calendered films are thinner, glossier, have better conformability and less shrinkage than calendered films made years ago.
- Greater production yields less cost
- Stiffer/thicker film equals easier handling
- Excellent performance on flat, simple and moderate curves
- Today's calendered films have a greater variety of colors as well as a wide range of gloss levels.
- Shrinkage of polymeric or high grade calendered films can be as low as 2-3%
- Formulation of film increases resistance to abrasion