High density polyethylene processing method

PE can be manufactured using a wide range of different processing methods. Using ethylene as the main raw material, propylene, 1-butene, and hexene as copolymers, under the action of a catalyst, the slurry polymerization or gas phase polymerization process is used, and the resulting polymer is flashed, separated, dried, granulated, etc. process to obtain a finished product with uniform particles. Including such processes as sheet extrusion, film extrusion, pipe or profile extrusion, blow molding, injection molding and rotational molding. HDPE is suitable for various molding processes of thermoplastic molding and has good molding processability, such as injection molding, extrusion, blow molding, rotational molding, coating, foaming process, thermoforming, heat sealing, heat welding, etc.
Extrusion: Grades used in extrusion production generally have a melt index of less than 1 and a medium to wide MWD. During processing, low MI can achieve suitable melt strength. Wider MWD grades are more suitable for extrusion because they have higher production speeds, lower die pressures and a reduced tendency to melt fracture.
PE has many extrusion applications such as wires, cables, hoses, pipes and profiles. Pipe applications range from small cross-section yellow pipes for natural gas to thick-walled black pipes for industrial and urban pipelines. Large diameter hollow wall pipes are growing rapidly as a replacement for storm drains and other sewer lines made of concrete.
Sheet and Thermoforming: The thermoformed liners of many large picnic coolers are made from PE, which offers toughness, light weight and durability. Other sheet and thermoformed products include fenders, tank liners, pan guards, shipping boxes and tanks. One large and rapidly growing sheet application is mulch or pond decking, which is based on MDPE for its toughness, chemical resistance and impermeability.
Blow molding: More than 1/3 of HDPE sold in the United States is used for blow molding. These range from bottles containing bleach, motor oil, detergent, milk and distilled water to large refrigerators, car fuel tanks and canisters. The properties of blow molding grades, such as melt strength, ES-CR and toughness, are similar to those used for sheet and thermoforming applications, so similar grades can be used.
Injection-blow molding is typically used to create smaller containers (less than 16oz) for packaging pharmaceuticals, shampoos and cosmetics. One advantage of this process is that the corners of the bottles are automatically removed, eliminating the need for post-finishing steps like ordinary blow molding. Medium to wide MWD grades are generally used, although there are certain narrow MWD grades used to improve surface finish.
Injection Molding: See "Material Properties" above.
Rotational molding: The material using this processing method is generally crushed into a powder material, which is melted and flowed in a thermal cycle. Rotational molding uses two types of PE: general purpose and cross-linkable. General-purpose MDPE/HDPE usually has a density range from 0.935 to 0.945g/CC, has a narrow MWD, giving the product high impact and minimal warpage, and its melt index range is generally 3-8. Higher MI grades are generally not suitable because they do not have the impact and environmental stress cracking resistance desired in rotomolded products.
Film: PE film processing generally uses ordinary blown film processing or cast extrusion processing. Most PE is used in films, either general-purpose low-density PE (LDPE) or linear low-density PE (LLDPE) available. HDPE film grade is generally used where superior stretchability and excellent impermeability are required. For example, HDPE films are commonly used in merchandise bags, grocery bags, and food packaging.