Like cast, calendered film also gets its name from the manufacturing process. The production of calendered film is similar to mixing and rolling out a pie dough. It is formulated with similar raw materials as cast. 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.
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.
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:
The chart below lists several attributes of cast and calendered films and how they compare to one another.
As with anything else, the finished product is only as good as what you put into it. This begins with choosing the right vinyl for the job. If you are doing a full vehicle wrap where you want the graphic to conform so that it looks and performs similar to paint you should choose a material with these characteristics, which would be cast film. Calendered films are ideal for applications that do not require the film to stretch or conform around complex contours. Examples of calendered film uses would be floor graphics, wall murals, window graphics, partial wraps and point-of-purchase displays.
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