Solvent Bandcast Process
Most thin gauged film is manufactured by the melt extrusion process, whereby the polymer is heated to its melting point in the barrel of a single or twin screw extruder, and, under pressure, forced out of a circular (blown film) or flat die (cast film). While the polymer is still in a molten state, it is physically pulled out of the die and drawn down to the required gauge. This draw down method actually lines up the molecules (orients the film) in the machine direction (cast film) or in both the machine and transverse direction (blown film). Therefore, all films have some orientation and under the right amount of heat will shrink back to their original form.

VCF Films, Inc., produces specialty PVC and other polymer films via a Solvent Bandcasting process. The steps in this process are:

• The polymer and appropriate additives are immersed in a highly reactive solvent which dissolves the polymer and forms a viscous "honey like" solution which we call "dope".
• Under pressure, the dope is continuously forced out of a flat die (similar to one used in extruded cast film) and is deposited onto a rotating, highly polished 300 foot stainless steel band.
• The ultimate gauge of the film is determined by a combination of the pressure at which the dope is forced out of the die and the speed of the rotating band.
• Once the dope is deposited on the band, it travels through a heated cabinet where the solvent is flashed off with only the polymer (film) remaining. Most of the vaporized solvent is then condensed and recovered in a sophisticated solvent recovery system.
• At the end of one complete 300 foot cycle, the film and band are cooled and the dried film is stripped from the band and wound up on a core.

Benefits of the Solvent Bandcast Process
Although a slow and costly process, Solvent Bandcasting produces film with certain unique characteristics and benefits, such as:

• Absolutely no thermal degradation of the polymer and, therefore, no loss of physical properties as the polymer is solvated and not melted.
• Little to no orientation of the film, and a very thermally stable end-product since the polymer is not "drawn down" to its final gauge. This is a benefit in certain laminations, particularly in products such as lidding stock and vacuum-formed applications.
• Pin-hole free film by the nature of the process. This makes it very suitable for specialty packaging applications such as liquids, chemicals, powders, etc.
• Because there is no heat history and very little pressure, most films manufactured via the solvent bandcast process have:
  • Minimal to no gels
  • No striations or other physical defects that affect optical properties
  • Excellent clarity
  • Ultra low haze
• Certain polymers, due to their molecular structure, are either too viscous or require too high a melt temperature to be extruded into thin film. Some of these polymers can be bandcast into thin gauged film as long as they can be solvated in the solvent utilized at VCF.

Most of the standard films manufactured by VCF can be printed, metallized, adhesive coated, heat laminated, vacuum formed, and/or thermoformed, utilizing conventional converting equipment.

A variety of standard grades of Solvent Bandcast films are currently available from VCF Films, and customized formulations can be developed based on the end use requirements.