Twenty Kinds of Plastics and Their Properties—(10) PE-LD
10.PE-LD low density polyethylene
Typical application: bowl, cabinet, pipe couplings
Injection molding process conditions:
Drying process: generally do not need
Melting temperature: 180~280 °C
Mold temperature: 20~40 degrees, in order to achieve uniform cooling and more economical to heat, cooling channels suggest a diameter of at least 8mm, and from the cooling cavity to the mold surface distance of not more than 1.5 times the diameter of the cooling chamber.
Injection pressure: maximum can reach 1500bar.
Pressure protection: maximum can reach 750bar.
Injection speed: it is recommended to use fast injection speed.
Runner and gate: various types of runner and gate can be used. PE-LD is especially suitable for the use of hot runner mold.
Chemical and physical properties:
The density of the commercial PE-LD materials is 0.91~0.94 g/cm3. PE-LD is permeable to gas and water vapor. The thermal expansion coefficient of PE-LD is very high not suitable for the processed products for long term use. If the density of PE-LD is between 0.91~0.925 g/cm3, its shrinkage rate is between 2%~5%. If the density is between 0.926~0.94 g/cm3, its shrinkage rate is between 1.5%~4%. The current actual shrinkage rate also depends on the injection process parameters. PE-LD can resist a variety of solvents at room temperature, but aromatic and chlorinated hydrocarbon solvents can expand it. Similar to PE-HD, environmental stress cracking is easy to occur in PE-LD.