Take you into the world of PE

1. PEPerformance: PE It is a plastic with the largest output among plastics.

Features—soft, non-toxic, cheap, easy to process, good chemical resistance, not easy to corrode, difficult to print.

PEPE is a typical crystalline high Polymers, commonly used ones are LDPE (low density polyethylene) and HDPE (high density polyethylene).

LDPE is softer (commonly known as soft rubber) HDPE is commonly known as hard soft rubber. It is harder than LDPE and is a semi-crystalline material with a smaller shrinkage after molding. High, between 1.5% and 4%, it has poor light transmittance and high crystallinity, and is prone to environmental stress cracking. The cracking phenomenon can be alleviated by using materials with very low flow characteristics to reduce internal stress. When the temperature is higher than 60°C, it is easily dissolved in hydrocarbon solvents, but its dissolution resistance is better than LDPE.

The high crystallinity of HDPE results in its high density, tensile strength, high temperature distortion temperature, viscosity and chemical stability. It has stronger penetration resistance than LDPE. PE-HD has lower impact strength. Properties are primarily controlled by density and molecular weight distribution. HDPE suitable for injection molding has a very narrow molecular weight distribution. For a density of 0.91~ 0.925g/cm3, we call it type PE-HD; for a density of 0.926~ 0.94g/cm3, it is called the second type HDPE; for a density of 0.94~ 0.965g/cm3, it is called Type II HDPE Type III HDPE. The material has good flow characteristics, with MFR ranging from 0.1 to 28. The higher the molecular weight.

LDPE has worse flow characteristics, but has better impact strength. HDPE is prone to environmental stress cracking. Cracking can be mitigated by using materials with very low flow characteristics to reduce internal stresses. HDPE is easily dissolved in hydrocarbon solvents when the temperature is higher than 60C, but its resistance to dissolution is better than LDPE. LDPE is a semi-crystalline material with a high shrinkage rate after molding, between 1.5% and 4%. The higher stretch resistance, penetration resistance, impact resistance and tear resistance of LLDPE (linear low density polyethylene) make LLDPE suitable for film. Its excellent resistance to environmental stress cracking, low temperature impact and warpage make LLDPE attractive for pipe, sheet extrusion and all molding applications. A new application of LLDPE is as a lining film for waste landfills and waste liquid ponds.

2. PE‘s process characteristics: The remarkable feature of PE parts is that they have a large molding shrinkage rate and are prone to shrinkage and deformation.

PEThe material has low water absorption and does not need to be dried. PE has a wide processing temperature range and is not easy to decompose (the decomposition temperature is 320°C). If the pressure Large, the product density is high and the shrinkage rate is small.

PEMedium fluidity, the processing conditions must be strictly controlled and the mold temperature should be kept constant (40-60℃).

PE is related to the molding process conditions. It has a higher cooling solidification temperature, and the lower the mold temperature, the lower the crystallinity. During the crystallization process, due to the anisotropy of shrinkage, internal stress concentration is caused. PE Deformation and cracking occur. Put the product in a water bath in 80℃ hot water, which can relax the pressure to a certain extent.

During the molding process, the material temperature should be higher and the injection pressure should be lower while ensuring the quality of the parts. The cooling is particularly required to be rapid and even, and the product will be hot when demolded.

HDPE drying: No need to dry if stored properly. Melting temperature 220~260C. For materials with larger molecules, melting is recommended.The temperature range is between 200~250C. Mold temperature: 50~95C. Plastic parts with a wall thickness below 6mm should use a higher mold temperature, and plastic parts with a wall thickness above 6mm should use a lower mold temperature. The cooling temperature of plastic parts should be uniform to reduce the difference in shrinkage. For optimal processing cycle time, the diameter of the cooling cavity should be no less than 8mm, and the distance from the mold surface should be within 1.3d (here “d” is the diameter of the cooling cavity).

Injection pressure: 700~1050bar. Injection speed: High-speed injection is recommended. Runner and gate: The runner diameter is between 4 and 7.5mm, and the runner length should be as short as possible. Various types of gates can be used, and the gate length should not exceed 0.75mm. Especially suitable for using hot runner molds.

LLDPE’s “soft when stretched” characteristic is a disadvantage in the film blowing process. The blown film bubble of LLDPE is not as thick as that of LDPE. Stablize. The die gap must be widened to avoid loss of throughput due to high back pressure and melt fracture.

The general die gap sizes of LDPE and LLDPE are 0.024-0.040 in and 0.060-0.10in respectively.

PEThe performance determinesPE tarpaulinThe absolute advantage in the market also makes it widely used in outdoor transportation and packaging protection.

(Part of the above content comes from the Internet)

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