Central Institute of Plastics Engineering & Technology, INDIA FILM EXTRUSION Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA Sheet & Flat film Extrusion Blown film Extrusion Central Institute of Plastics Engineering & Technology, INDIA

Sheet and Flat film Extrusion Sheet and flat films are produced for different purposes such as packaging, sun control film, electrical insulation, flat tape for woven sacks etc. A coat hanger die is used in order to make flat films. The transparency is achieved by quenching the molten film onto the chill roll. As such the cast film so formed is not of any use. It needs to be further oriented. Central Institute of Plastics Engineering & Technology, INDIA

Sheet and flat film – making plant Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA Flat Film Die Central Institute of Plastics Engineering & Technology, INDIA

Clothes hanger die for sheet extrusion Central Institute of Plastics Engineering & Technology, INDIA

Sheet Thickness Definitions Film : < 254 μm Thin sheet : 254 μm to 1500 μm Thick sheet : > 1500 μm Central Institute of Plastics Engineering & Technology, INDIA

Application of film & sheet Wall covering Signs Clear sheet as a substitute of glass Thermoforming Truck bed liners Protective packaging Toys Disposable drinking cups Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA For cooling, the sheet melt is wrapped around a series of cooling and finishing rolls. These rolls, which are usually filled with filled water, cool the sheet or flat film and give the surface a smooth finish. The downstream equipments are puller, orienter and the winders. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The thickness of the sheet and film is set by the combination of extruder speed, die gap and the relative speeds of the rollers and pullers. This process of controlling the thickness is technically called ‘drawing’. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The Drawing orients the molecules of the cast sheet or film into the machine direction. The sheets therefore have more strength in the machine direction than in the transverse direction. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA In certain films, the strength in transverse direction is also desired . This is done by mechanically grasping along their edges and pulled sideways after heating above Tg. Such sheets or films are called Biaxially oriented films. Central Institute of Plastics Engineering & Technology, INDIA

Transverse Direction Orientation Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The biaxially oriented films have strengths that can be twice as high as nonoriented films and sheets. The transparency is also very good in such films. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA Blown Film Extrusion Blown film extrusion technique is used to manufacture the film for carry bags, garbage bags and other high volume thin walled film materials. The polymer melt flows through a tubular die, which is like a combination of an offset die and a pipe die. Central Institute of Plastics Engineering & Technology, INDIA

Blown Film Extrusion Line Central Institute of Plastics Engineering & Technology, INDIA

A multi-story blown film line Central Institute of Plastics Engineering & Technology, INDIA

Curaway of a typical spiral-mandrel film extrusion die Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The polymer melt flows around a mandrel and exits the die as a tube vertically upwards. A cooling ring is placed at the exit of the die to give the tube some dimensional stability. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA Since the melt is air-cooled, the polymer gets some time for crystallizing and hence the transparency is effected. In blown film extrusion, therefore, the hazy film is obtained. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The tube is called bubble, which is taken off by the take off rollers or drawn above for orientation. This tube is also blown by air, which remains locked inside the bubble. This air maintains the width of the bubble and at the same time orients the film in hoop direction. Central Institute of Plastics Engineering & Technology, INDIA

MULTILAYER FILM EXTRUSION Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA This is the process that joins two or more streams of molten plastics into a single extrudate stream in such a way that the materials bond together but do not mix. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA Co-extrusion Die Central Institute of Plastics Engineering & Technology, INDIA

Another view of Coextrusion die Central Institute of Plastics Engineering & Technology, INDIA

Sheet Die with feed block for coextrusion Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA A separate extruder is needed for each stream and then the extruders are linked so that the extrudates can flow together in a way that is appropriate for the particular application. Central Institute of Plastics Engineering & Technology, INDIA

Central Institute of Plastics Engineering & Technology, INDIA The coextruded films are made by using flat film die as well as blown film die. But most commonly blown film dies are used. Central Institute of Plastics Engineering & Technology, INDIA