HDPE Bottles and Containers
Blow molding is used by Takween to manufacture white and natural polyethylene and clear bottles (discussed above) ranging from 200 ml to 20 liters in capacity. The bottles are used in the dairies and beverages industries and thus require high quality products. HDPE and PP bottles compete with PET.
The blow molding process has essentially two stages in one process. In the first stage a preform of the hot plastic resin is formed with a hole in one end to pass compressed air through. In the second stage the compressed air expands the hot preform and presses it against a mold cavity. The pressure is held until the plastic cools – say, for 6 to 8 seconds. The mold then opens up and ejects the cooled, hardened plastic.
The three main types of blow molding are extrusion, injection and stretch blow molding. The extrusion process is widely used in the drinks and beverages industry. In extrusion blow molding there are continuous and the intermittent process technologies. The injected molded process is only used for small capacity bottles and is more difficult to control than extrusion as the plastic material is injected onto a core pin for subsequent blow molding rather than extruded into a hollow tube in the extrusion process. The stretch blow molding process first involves injection molding of preforms and then blow molding and can produce high volumes with limited restrictions on bottle design.