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FLAT-DIE AND CAST-ON-CARRIER EXTRUSION

WHAT IS FLAT-DIE EXTRUSION?

Argotec's flat-die extrusion process begins with computerized mixing of virgin resin with additives to control film process and properties, along with carefully controlled rates of regrind, if necessary, to reduce customer cost. Any regrind used is generated in-house to ensure quality.

The blend of materials is melted and conveyed through the extruder. The heated material is then forced, under pressure, through a flat, horizontal die slit.

The gauge of the film is controlled by adjustments made at regular intervals across the width of the die. The film cools at the die exit as it passes through the chilled nip rolls. It is trimmed to the specified width prior to being wound onto corrugated or plastic cores, wrapped and packaged for shipment.

Depending on the secondary fabrication requirements, physical properties or end-use of the film, interleafs such as polyester film, single or double polyethylene film (DPE), or paper may be inserted prior to final winding to assist in handling or to prevent blocking.

HOW DOES CAST-ON-CARRIER DIFFER
FROM FLAT-DIE EXTRUSION?

Cast-on-carrier extrusion is a variation of the flat-die process that is used when:

• Film is so thin it requires support to handle.
• Secondary fabrication requires the use of a carrier.
• The surface finish of the film needs to be preserved.

The initial phases of the cast-on-carrier process are identical to flat-die extrusion. The process differs because the carrier is introduced at the die instead of at wind up. Since the film is warm at the die exit, it takes on the surface finish of the carrier. Typical carriers are polyester film, polyethylene film and paper.

The film-on-carrier is then conveyed through chilled rollers, slitting and winding, as with the flat-die process.

WHY FLAT DIE & AND CAST-ON-CARRIER
EXTRUSION IS SUPERIOR TO BLOWN FILM

Films produced via flat-die and cast-on-carrier extrusion technologies are considered higher quality than product manufactured using blown film extrusion because:

• They contain less gel. Gel can be unmelted resin or resin particles with slightly different melt properties. Gel can effect mechanical and aesthetic properties.
• No processing aids or lubricants are required. These processing aids can affect adhesive wet-out. Lubricants can interfere with downstream processing, such as lamination or printing.
• Gauge can be adjusted in-line.
• Surface finish can be controlled.
• Extremely thin films can be extruded using the cast-on-carrier option, to thicknesses as low as 0.2 mil.
• Thick films up to 125 mils can be produced.
• One or more interleafs/carriers may be used for cleanness or other reasons.

When run in Argotec's multi-atmospheric, hard-wall, clean-room manufacturing facilities, flat-die extrusion reduces virtually all contaminants, air-borne and otherwise, for the cleanest possible film.

WHEN TO USE BLOWN FILM

In certain cases, there may be advantages to using blown film extrusion. For example:

• When cost is a factor. Blown film is the most economical method for producing films from 1-10 mils thick.
• When a carrier or interleaf is not required.
• When a smooth surface is acceptable.
• When gloss or matte finish is not required.
• When even roll put-up is critical. The rotating die on a blown film extruder distributes any gauge variations evenly across the width of the roll.
• In some applications, the high-slip attribute of the processing aid is desirable.

However, when these factors do not exist, flat-die or cast-on-carrier will typically be the preferred extrusion method.

When choosing a specialty film supplier, be sure to consider the entire program. Click on the link below for a review of what should be included in a successful flat-die or cast-on-carrier film program.