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The predominant raw material in this process is polyethylene, most of it LDPE, some LLDPE, and for paper-like films - high-molecular weight HDPE. A few examples of the applications of blown film include packaging from snack to shopping bags, shrink film, stretch wrap, agriculture films, building films, multi-layer films, protective films and hundreds of other products.
This, again, is a process wher Telford Smith's broad range of extruders maximise line performance necessary for the profitable production of lay-flat tubing, shrink film or sheeting.
Low barrel centre line heights are required to utilise the full cooling availability of the tower height from the die face to the upper nip roll. Telford Smith Engineering manufacture extruders constructed especially for this application with side mounted blowers and drive motors to minimise height, maximise cooling and increase line speeds.
Blown film extruder screws lend themselves perfectly to Telford Smith Engineering barrier designs. In contrast to conventional screws wher solids become suspended in the melt pool, the barrier flight (intermediate flight) is used to segregate the melted polymer from the solids, and provide separate treatment for the solid and liquid component. The net result is a more comprehensive melting process that permits use of deeper final metering channels with higher corresponding metering rates (higher outputs). Consequently melt temperature is reduced and temperature uniformity is improved. Since less heat is generated to complete the melt with a barrier screw energy saving occurs.
Co-extrusion as the name implies relates to the extrusion of two or more polymer layers through a common die. Extruder design is the same as that for mono extrusion with some minor but important design changes. These are mobility and height adjustment. Mobility is required to allow for thermal expansion and contraction of the extruder barrel. Height adjustment is necessary to precisely align the extruder with the die adaptors and prevent polymer leakage. Telford Smith Engineering have addressed these aspects and designed a wheel box with built in height adjustment and a small amount of lateral (side) movement. This has resulted in a user-friendly system meeting this criterion.
Screw design for the primary layers would be as per mono extrusion. For the barrier and adhesive layers (typically E V O H, Nylon and Ionomers) a different approach to screw design must be adopted. Telford Smith Engineering has the experience and technology that is essential in ensuring these sensitive polymers are not contaminated during extrusion. Superior screw design, maintains a high level of processability and film quality.
Extrusion Blown Film Lines