PP polypropylene injection molding characteristics

PP polypropylene injection molding characteristics

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

Injection molding process conditions:
Drying treatment: Drying is not required if stored properly.
Melting temperature: 220~275C, please 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: Generally, high-speed injection molding can be used to minimize internal pressure. If there is a defect on the surface of the product,
Then use low speed injection molding at higher temperatures.
Runners and gates: For cold runners, typical runner diameters range from 4 to 7 mm. It is recommended to use a round inlet and flow path. 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. The hot runner system is fully available for PP materials.

Chemical and physical properties:
PP is a semi-crystalline material. It is harder and has a higher melting point than PE.
Since the PP temperature of the homopolymer type is very brittle when it is higher than 0 C, many commercial PP materials are random copolymers of 1 to 4% of ethylene or a clamp copolymer of a higher ratio of ethylene. The copolymer type PP material has a low heat distortion temperature (100C), low transparency, low gloss, low rigidity, but has stronger impact strength. The strength of PP increases as the ethylene content increases.
The Vicat softening temperature of PP is 150C. Due to the high degree of crystallinity, this material has excellent surface stiffness and scratch resistance.
There is no environmental stress cracking problem in PP. Typically, PP is modified by the addition of glass fibers, metal additives or thermoplastic rubber. The flow rate of PP has a MFR ranging from 1 to 40. Low MFR PP materials have better impact resistance but lower elongation. For materials of the same MFR, the strength of the copolymer type is higher than that of the homopolymer type.
Due to crystallization, the shrinkage rate of PP is quite high, generally 1.8 to 2.5%. And the direction uniformity of shrinkage is much better than materials such as PE-HD. The addition of 30% glass additive can reduce the shrinkage to 0.7%. Both the homopolymer type and the copolymer type PP materials have excellent moisture absorption resistance, acid and alkali corrosion resistance, and solubility resistance. However, it is not resistant to aromatic hydrocarbons such as benzene solvents, chlorinated hydrocarbons (carbon tetrachloride) solvents, and the like. PP does not have oxidation resistance at high temperatures like PE.

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