PP polypropylene injection molding properties

PP polypropylene injection molding properties

Typical application range:
Automotive industry (mainly using PP with metal additives: fenders, ventilation ducts, fans, etc.), instruments (dishwasher door liners, dryer ventilation ducts, washing machine frames and covers, refrigerator door liners, etc.), Japan Use consumer products (lawn and garden equipment such as lawn mowers, sprinklers, etc.).

Injection Molding Process Conditions:
Drying: Drying is not required if stored properly.
Melting temperature: 220 ~ 275C, be careful not to exceed 275C.
Mold temperature: 40~80C, 50C is recommended. The degree of crystallization is mainly determined by the mold temperature.
Injection pressure: up to 1800 bar.
Injection speed: In general, using high-speed injection molding can minimize internal pressure. If there is a defect on the surface of the product,
Then use low speed injection at higher temperatures.
Runners and Gates: For cold runners, typical runner diameters range from 4 to 7 mm. It is recommended to use round injection ports and runners. All types of gates can be used. Typical gate diameters range from 1 to 1.5 mm, but gates as small as 0.7 mm can also be used. For edge gates, the minimum gate depth should be half the wall thickness; the minimum gate width should be at least twice the wall thickness. PP material can use hot runner system completely.

Chemical and physical properties:
PP is a semi-crystalline material. It is harder and has a higher melting point than PE.
Since the homopolymer PP is brittle at temperatures above 0C, many commercial PP materials are random copolymers with 1 to 4% ethylene or clamp copolymers with higher ethylene content. Copolymer PP materials have a low heat distortion temperature (100C), low transparency, low gloss, and low rigidity, but have stronger impact strength. The strength of PP increases with the ethylene content.
The Vicat softening temperature of PP is 150C. Due to the high degree of crystallinity, this material has very good surface stiffness and scratch resistance.
PP does not have the problem of environmental stress cracking. In general, PP is modified by adding glass fibers, metal additives, or thermoplastic rubber. The flow rate of PP has an MFR range of 1 to 40. PP materials with low MFR have better impact resistance but lower strength. For the same MFR material, the copolymer type has higher strength than the homopolymer type.
Due to crystallization, PP shrinkage is quite high, typically 1.8 to 2.5%. And the uniformity of the shrinkage direction is much better than that of materials such as PE-HD. Adding 30% of the glass additive can reduce the shrinkage to 0.7%. Homopolymer and copolymer PP materials have excellent resistance to moisture absorption, acid and alkali corrosion, and resistance to dissolution. However, it is not resistant to aromatic hydrocarbons such as benzene solvents, chlorinated hydrocarbon (carbon tetrachloride) solvents, and the like. PP is also not as resistant to PE as it is at high temperatures.

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