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

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

3. 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

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

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

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

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

8. 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

9. 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

10. 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

11. 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

12. 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

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

14. 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

15. 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

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

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

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

19. 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

20. 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

21. 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

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

23. 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

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

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

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

27. 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

28. 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