hdpe process conditions and physical and chemical properties

HDPE (High Density Polyethylene)

Injection molding process conditions:

Drying: No drying required if stored properly.

Melting temperature: 220~260℃. For varieties with larger molecules, the recommended melting temperature range is between 200 and 250 °C.

Mold temperature: 50~95℃. Plastic parts with wall thicknesses above 6mm use lower mold temperatures. The cooling temperature of the plastic part should be uniform to reduce the difference in shrinkage. In order to obtain a reasonable molding cycle, the diameter of the cooling circuit should not be less than 8mm, and the distance from the mold surface should be within 1.3d (d is the diameter of the cooling circuit).

Injection pressure: 70~105MPa

Injection speed: It is recommended to use high-speed injection

Runner and gate: The diameter of the runner should be between 4 and 7.5mm, and the length of the runner should be as short as possible. Various types of gates can be used, and the gate length should not exceed 0.75mm. This resin is particularly suitable for use with hot runners.

Chemical and Physical Properties:

The high crystallinity of HDPE results in its high density. HDPE has stronger permeation resistance than LDPE. HDPE has a narrow molecular weight distribution. The density is

0.91~0.925g/cm³, called the first type HDPE; the density is 0.926~0.94g/cm³, called the second type HDPE; the density is 0.94~

0.965g/cm³, called the third type HDPE. The flow of this material is very good, and the MFR is between 0.1 and 28. The higher the molecular weight, the poorer the flow of HDPE, but the better impact strength.

HDPE is a semi-crystalline material, and the molding shrinkage rate is large, between 1.5% and 4%. HDPE is prone to environmental stress cracking. Usually, varieties with very low flow characteristics are used to reduce the internal stress of the molded plastic parts, thereby reducing the cracking phenomenon. However, in the environment where the temperature is higher than 60 °C, the plastic parts formed by HDPE are easily dissolved in hydrocarbon solvents, but their resistance to dissolution is better than that of LDPE.

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